diff --git a/fixposition_driver_lib/include/fixposition_driver_lib/msg_data.hpp b/fixposition_driver_lib/include/fixposition_driver_lib/msg_data.hpp
index ff38989..a4ed53c 100644
--- a/fixposition_driver_lib/include/fixposition_driver_lib/msg_data.hpp
+++ b/fixposition_driver_lib/include/fixposition_driver_lib/msg_data.hpp
@@ -140,7 +140,8 @@ struct GpggaData {
     double altitude;
     Eigen::Matrix<double, 3, 3> cov;
     int position_covariance_type;
-    GpggaData() : latitude(0.0), longitude(0.0), altitude(0.0), position_covariance_type(0) { cov.setZero(); }
+    bool valid;
+    GpggaData() : latitude(0.0), longitude(0.0), altitude(0.0), position_covariance_type(0), valid(false) { cov.setZero(); }
 };
 
 struct GpzdaData {
@@ -148,7 +149,8 @@ struct GpzdaData {
     std::string time;
     std::string date;
     times::GpsTime stamp;
-    GpzdaData() : time(""), date("") {}
+    bool valid;
+    GpzdaData() : time(""), date(""), valid(false) {}
 };
 
 struct GprmcData {
@@ -159,7 +161,8 @@ struct GprmcData {
     double longitude;
     double speed;
     double course;
-    GprmcData() : latitude(0.0), longitude(0.0), speed(0.0), course(0.0) {}
+    bool valid;
+    GprmcData() : latitude(0.0), longitude(0.0), speed(0.0), course(0.0), valid(false) {}
 };
 
 }  // namespace fixposition
diff --git a/fixposition_driver_lib/src/gpgga.cpp b/fixposition_driver_lib/src/gpgga.cpp
index 52e129a..94bbcb5 100644
--- a/fixposition_driver_lib/src/gpgga.cpp
+++ b/fixposition_driver_lib/src/gpgga.cpp
@@ -45,6 +45,14 @@ void GpggaConverter::ConvertTokens(const std::vector<std::string>& tokens) {
         return;
     }
 
+    // Check that critical message fields are populated
+    for (int i = 1; i < 11; i++) {
+        if (tokens.at(i).empty()) {
+            msg_ = GpggaData();
+            return;
+        }
+    }
+
     // Header stamps
     msg_.time = tokens.at(time_idx);
 
@@ -73,6 +81,9 @@ void GpggaConverter::ConvertTokens(const std::vector<std::string>& tokens) {
     msg_.cov(1, 2) = msg_.cov(2, 1) = 0.0;
     msg_.position_covariance_type = 1; // COVARIANCE_TYPE_APPROXIMATED
 
+    // Set message as valid
+    msg_.valid = true;
+
     // Process all observers
     for (auto& ob : obs_) {
         ob(msg_);
diff --git a/fixposition_driver_lib/src/gprmc.cpp b/fixposition_driver_lib/src/gprmc.cpp
index 4d6a6f4..b1bf2a8 100644
--- a/fixposition_driver_lib/src/gprmc.cpp
+++ b/fixposition_driver_lib/src/gprmc.cpp
@@ -46,6 +46,14 @@ void GprmcConverter::ConvertTokens(const std::vector<std::string>& tokens) {
         return;
     }
 
+    // Check that critical message fields are populated
+    for (int i = 1; i < 9; i++) {
+        if (tokens.at(i).empty()) {
+            msg_ = GprmcData();
+            return;
+        }
+    }
+
     // Header stamps
     msg_.time = tokens.at(time_idx);
 
@@ -67,6 +75,9 @@ void GprmcConverter::ConvertTokens(const std::vector<std::string>& tokens) {
     // Get GPS status
     msg_.mode = tokens.at(mode_idx);
 
+    // Set message as valid
+    msg_.valid = true;
+
     // Process all observers
     for (auto& ob : obs_) {
         ob(msg_);
diff --git a/fixposition_driver_lib/src/gpzda.cpp b/fixposition_driver_lib/src/gpzda.cpp
index e774de8..298cb32 100644
--- a/fixposition_driver_lib/src/gpzda.cpp
+++ b/fixposition_driver_lib/src/gpzda.cpp
@@ -69,7 +69,7 @@ void convertToGPSTime(const std::string& utcTimeString, std::string& gpsWeek, st
     double gpsTime = std::fmod(timeDifference, secondsInWeek);
 
     // Add milliseconds to GPS time
-    gpsTime += (18 + ms);
+    gpsTime += (fixposition::times::Constants::gps_leap_time_s + ms);
 
     // Convert results to strings
     std::ostringstream ossWeek, ossTime;
@@ -89,6 +89,14 @@ void GpzdaConverter::ConvertTokens(const std::vector<std::string>& tokens) {
         return;
     }
 
+    // Check that critical message fields are populated
+    for (int i = 1; i < 6; i++) {
+        if (tokens.at(i).empty()) {
+            msg_ = GpzdaData();
+            return;
+        }
+    }
+
     // Populate time fields
     msg_.time = tokens.at(time_idx);
     msg_.date = tokens.at(day_idx) + '/' + tokens.at(month_idx) + '/' + tokens.at(year_idx);
@@ -99,6 +107,9 @@ void GpzdaConverter::ConvertTokens(const std::vector<std::string>& tokens) {
     convertToGPSTime(utcTimeString, gps_week, gps_tow);
     msg_.stamp = ConvertGpsTime(gps_week, gps_tow);
 
+    // Set message as valid
+    msg_.valid = true;
+
     // Process all observers
     for (auto& ob : obs_) {
         ob(msg_);
diff --git a/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp b/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
index 13dc590..f7e6ace 100644
--- a/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
+++ b/fixposition_driver_ros1/include/fixposition_driver_ros1/fixposition_driver_node.hpp
@@ -61,8 +61,12 @@ class FixpositionDriverNode : public FixpositionDriver {
          * @brief Construct a new Fixposition Driver Node object
          */
         bool checkEpoch() {
-            if ((gpgga.time.compare(gpzda.time) == 0) && (gpgga.time.compare(gprmc.time) == 0)) {
-                return true;
+            if (gpgga.valid && gpgga.valid && gpgga.valid) {
+                if ((gpgga.time.compare(gpzda.time) == 0) && (gpgga.time.compare(gprmc.time) == 0)) {
+                    return true;
+                } else {
+                    return false;
+                }
             } else {
                 return false;
             }
diff --git a/fixposition_driver_ros1/src/data_to_ros1.cpp b/fixposition_driver_ros1/src/data_to_ros1.cpp
index fb8fc54..29378fe 100644
--- a/fixposition_driver_ros1/src/data_to_ros1.cpp
+++ b/fixposition_driver_ros1/src/data_to_ros1.cpp
@@ -17,7 +17,12 @@
 
 namespace fixposition {
 void ImuDataToMsg(const ImuData& data, sensor_msgs::Imu& msg) {
-    msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = ros::Time::now();
+    } else {
+        msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    }
+    
     msg.header.frame_id = data.frame_id;
     tf::vectorEigenToMsg(data.linear_acceleration, msg.linear_acceleration);
     tf::vectorEigenToMsg(data.angular_velocity, msg.angular_velocity);
@@ -29,7 +34,12 @@ void NavSatStatusDataToMsg(const NavSatStatusData& data, sensor_msgs::NavSatStat
 }
 
 void NavSatFixDataToMsg(const NavSatFixData& data, sensor_msgs::NavSatFix& msg) {
-    msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = ros::Time::now();
+    } else {
+        msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    }
+
     msg.header.frame_id = data.frame_id;
     NavSatStatusDataToMsg(data.status, msg.status);
     msg.latitude = data.latitude;
@@ -60,7 +70,12 @@ void TwistWithCovDataToMsg(const fixposition::TwistWithCovData& data, geometry_m
 }
 
 void OdometryDataToMsg(const fixposition::OdometryData& data, nav_msgs::Odometry& msg) {
-    msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = ros::Time::now();
+    } else {
+        msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    }
+
     msg.header.frame_id = data.frame_id;
     msg.child_frame_id = data.child_frame_id;
 
@@ -69,7 +84,12 @@ void OdometryDataToMsg(const fixposition::OdometryData& data, nav_msgs::Odometry
 }
 
 void VrtkDataToMsg(const VrtkData& data, fixposition_driver_ros1::VRTK& msg) {
-    msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = ros::Time::now();
+    } else {
+        msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.stamp));
+    }
+    
     msg.header.frame_id = data.frame_id;
     msg.pose_frame = data.pose_frame;
     msg.kin_frame = data.kin_frame;
diff --git a/fixposition_driver_ros1/src/fixposition_driver_node.cpp b/fixposition_driver_ros1/src/fixposition_driver_node.cpp
index 161426c..209741e 100644
--- a/fixposition_driver_ros1/src/fixposition_driver_node.cpp
+++ b/fixposition_driver_ros1/src/fixposition_driver_node.cpp
@@ -94,7 +94,11 @@ void FixpositionDriverNode::RegisterObservers() {
                     }
                     if (eul_pub_.getNumSubscribers() > 0) {
                         geometry_msgs::Vector3Stamped ypr;
-                        ypr.header.stamp = ros::Time::fromBoost(fixposition::times::GpsTimeToPtime(data.odometry.stamp));
+                        if (data.odometry.stamp.tow == 0.0 && data.odometry.stamp.wno == 0) {
+                            ypr.header.stamp = ros::Time::now();
+                        } else {
+                            ypr.header.stamp = ros::Time::fromBoost(fixposition::times::GpsTimeToPtime(data.odometry.stamp));
+                        }
                         ypr.header.frame_id = "FP_POI";
                         tf::vectorEigenToMsg(data.eul, ypr.vector);
                         eul_pub_.publish(ypr);
@@ -197,7 +201,11 @@ void FixpositionDriverNode::PublishNmea(NmeaMessage data) {
         fixposition_driver_ros1::NMEA msg;
         
         // ROS Header
-        msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.gpzda.stamp));
+        if (data.gpzda.stamp.tow == 0.0 && data.gpzda.stamp.wno == 0) {
+            msg.header.stamp = ros::Time::now();
+        } else {
+            msg.header.stamp = ros::Time::fromBoost(GpsTimeToPtime(data.gpzda.stamp));
+        }
         msg.header.frame_id = "LLH";
         
         // Latitude [degrees]. Positive is north of equator; negative is south
diff --git a/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp b/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
index 6573259..1df89e5 100644
--- a/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
+++ b/fixposition_driver_ros2/include/fixposition_driver_ros2/fixposition_driver_node.hpp
@@ -64,12 +64,16 @@ class FixpositionDriverNode : public FixpositionDriver {
          * @brief Check if GNSS epoch is complete
          */
         bool checkEpoch() {
-            if ((gpgga.time.compare(gpzda.time) == 0) && (gpgga.time.compare(gprmc.time) == 0)) {
-                return true;
+            if (gpgga.valid && gpgga.valid && gpgga.valid) {
+                if ((gpgga.time.compare(gpzda.time) == 0) && (gpgga.time.compare(gprmc.time) == 0)) {
+                    return true;
+                } else {
+                    return false;
+                }
             } else {
                 return false;
             }
-        }  
+        }
     };
 
    private:
diff --git a/fixposition_driver_ros2/src/data_to_ros2.cpp b/fixposition_driver_ros2/src/data_to_ros2.cpp
index 14f626d..3860e17 100644
--- a/fixposition_driver_ros2/src/data_to_ros2.cpp
+++ b/fixposition_driver_ros2/src/data_to_ros2.cpp
@@ -25,7 +25,11 @@
 
 namespace fixposition {
 void ImuDataToMsg(const ImuData& data, sensor_msgs::msg::Imu& msg) {
-    msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = rclcpp::Clock().now();
+    } else {
+        msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    }
     msg.header.frame_id = data.frame_id;
 
     tf2::toMsg(data.linear_acceleration, msg.linear_acceleration);
@@ -38,7 +42,11 @@ void NavSatStatusDataToMsg(const NavSatStatusData& data, sensor_msgs::msg::NavSa
 }
 
 void NavSatFixDataToMsg(const NavSatFixData& data, sensor_msgs::msg::NavSatFix& msg) {
-    msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = rclcpp::Clock().now();
+    } else {
+        msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    }
     msg.header.frame_id = data.frame_id;
     NavSatStatusDataToMsg(data.status, msg.status);
     msg.latitude = data.latitude;
@@ -69,7 +77,11 @@ void TwistWithCovDataToMsg(const fixposition::TwistWithCovData& data, geometry_m
 }
 
 void OdometryDataToMsg(const fixposition::OdometryData& data, nav_msgs::msg::Odometry& msg) {
-    msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = rclcpp::Clock().now();
+    } else {
+        msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    }
     msg.header.frame_id = data.frame_id;
     msg.child_frame_id = data.child_frame_id;
 
@@ -78,7 +90,11 @@ void OdometryDataToMsg(const fixposition::OdometryData& data, nav_msgs::msg::Odo
 }
 
 void VrtkDataToMsg(const VrtkData& data, fixposition_driver_ros2::msg::VRTK& msg) {
-    msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    if (data.stamp.tow == 0.0 && data.stamp.wno == 0) {
+        msg.header.stamp = rclcpp::Clock().now();
+    } else {
+        msg.header.stamp = GpsTimeToMsgTime(data.stamp);
+    }
     msg.header.frame_id = data.frame_id;
     msg.pose_frame = data.pose_frame;
     msg.kin_frame = data.kin_frame;
diff --git a/fixposition_driver_ros2/src/fixposition_driver_node.cpp b/fixposition_driver_ros2/src/fixposition_driver_node.cpp
index 7c1d2b9..bef831c 100644
--- a/fixposition_driver_ros2/src/fixposition_driver_node.cpp
+++ b/fixposition_driver_ros2/src/fixposition_driver_node.cpp
@@ -115,7 +115,11 @@ void FixpositionDriverNode::RegisterObservers() {
                     }
                     if (eul_pub_->get_subscription_count() > 0) {
                         geometry_msgs::msg::Vector3Stamped ypr;
-                        ypr.header.stamp = GpsTimeToMsgTime(data.odometry.stamp);
+                        if (data.odometry.stamp.tow == 0.0 && data.odometry.stamp.wno == 0) {
+                            ypr.header.stamp = rclcpp::Clock().now();
+                        } else {
+                            ypr.header.stamp = GpsTimeToMsgTime(data.odometry.stamp);
+                        }
                         ypr.header.frame_id = "FP_POI";
                         ypr.vector.set__x(data.eul.x());
                         ypr.vector.set__y(data.eul.y());
@@ -222,7 +226,11 @@ void FixpositionDriverNode::PublishNmea(NmeaMessage data) {
         fixposition_driver_ros2::msg::NMEA msg;
         
         // ROS Header
-        msg.header.stamp = GpsTimeToMsgTime(data.gpzda.stamp);
+        if (data.gpzda.stamp.tow == 0.0 && data.gpzda.stamp.wno == 0) {
+            msg.header.stamp = rclcpp::Clock().now();
+        } else {
+            msg.header.stamp = GpsTimeToMsgTime(data.gpzda.stamp);
+        }
         msg.header.frame_id = "LLH";
         
         // Latitude [degrees]. Positive is north of equator; negative is south