diff --git a/OpenActive.NET.Test/OrderTest.cs b/OpenActive.NET.Test/OrderTest.cs
index 378f11c..b23eb9b 100644
--- a/OpenActive.NET.Test/OrderTest.cs
+++ b/OpenActive.NET.Test/OrderTest.cs
@@ -197,7 +197,9 @@ public void OrderQuote_EncodeDecode()
                 "\"orderedItem\":{" +
                     "\"@type\":\"ScheduledSession\"," +
                     "\"@id\":\"https://example.com/events/452/subEvents/132\"," +
+                    "\"startDate\":\"2018-10-30T11:00:00+00:00\"," +
                     "\"identifier\":123," +
+                    "\"endDate\":\"2018-10-30T12:00:00+00:00\"," +
                     "\"superEvent\":{" +
                         "\"@type\":\"SessionSeries\"," +
                         "\"@id\":\"https://example.com/events/452\"," +
@@ -228,9 +230,7 @@ public void OrderQuote_EncodeDecode()
                         "}" +
                     "}," +
                     "\"duration\":\"PT1H\"," +
-                    "\"eventStatus\":\"https://schema.org/EventScheduled\"," +
-                    "\"startDate\":\"2018-10-30T11:00:00+00:00\"," +
-                    "\"endDate\":\"2018-10-30T12:00:00+00:00\"" +
+                    "\"eventStatus\":\"https://schema.org/EventScheduled\"" +
                 "}," +
                 "\"orderItemStatus\":\"https://openactive.io/OrderItemConfirmed\"," +
                 "\"unitTaxSpecification\":[" +
@@ -331,7 +331,7 @@ public void Order_Deserialize_Accessors()
             Assert.Equal("Geoff", order?.Customer.GivenName);
             Assert.Equal("EUCODE", order?.OrderedItem?[0]?.UnitTaxSpecification?[0]?.Identifier.GetClass<List<PropertyValue>>()?[0].Name);
             Assert.Equal(new TimeSpan(6,0,0,0), order?.OrderedItem?[0]?.AcceptedOffer?.ValidFromBeforeStartDate);
-            Assert.Equal(new DateTimeOffset(2018, 10, 30, 11, 00, 00, 00, new TimeSpan()), order?.OrderedItem?[0]?.OrderedItem?.StartDate.GetPrimative<DateTimeOffset>());
+            Assert.Equal(new DateTimeOffset(2018, 10, 30, 11, 00, 00, 00, new TimeSpan()), ((ScheduledSession)order?.OrderedItem?[0]?.OrderedItem)?.StartDate);
         }
 
         [Fact]
diff --git a/OpenActive.NET/models/ScheduledSession.cs b/OpenActive.NET/models/ScheduledSession.cs
index f327af6..d35c141 100644
--- a/OpenActive.NET/models/ScheduledSession.cs
+++ b/OpenActive.NET/models/ScheduledSession.cs
@@ -44,13 +44,38 @@ public override string ToString()
         [DataMember(Name = "@type", Order = 1)]
         public override string Type => "ScheduledSession";
 
+        /// <summary>
+        /// The start date and time of the event.
+        /// </summary>
+        /// <example>
+        /// <code>
+        /// "startDate": "2018-01-27T12:00:00Z"
+        /// </code>
+        /// </example>
+        [DataMember(Name = "startDate", EmitDefaultValue = false, Order = 7)]
+        [JsonConverter(typeof(OpenActiveDateTimeOffsetToISO8601DateTimeValuesConverter))]
+        public new virtual DateTimeOffset? StartDate { get; set; }
+
+        /// <summary>
+        /// The end date and time of the event.
+        /// It is recommended that publishers provide either an schema:endDate or a schema:duration for an event.
+        /// </summary>
+        /// <example>
+        /// <code>
+        /// "endDate": "2018-01-27T12:00:00Z"
+        /// </code>
+        /// </example>
+        [DataMember(Name = "endDate", EmitDefaultValue = false, Order = 8)]
+        [JsonConverter(typeof(OpenActiveDateTimeOffsetToISO8601DateTimeValuesConverter))]
+        public new virtual DateTimeOffset? EndDate { get; set; }
+
         [Obsolete("This property is disinherited in this type, and must not be used.", true)]
         public override List<Event> SubEvent { get; set; }
 
         /// <summary>
         /// Relates a child event to a parent event. Properties describing the parent event can be assumed to apply to the child, unless otherwise specified. A parent event might specify a recurring schedule, of which the child event is one specific instance
         /// </summary>
-        [DataMember(Name = "superEvent", EmitDefaultValue = false, Order = 8)]
+        [DataMember(Name = "superEvent", EmitDefaultValue = false, Order = 10)]
         [JsonConverter(typeof(ValuesConverter))]
         public new virtual SingleValues<Uri, Event> SuperEvent { get; set; }
     }
diff --git a/OpenActive.NET/models/SessionSeries.cs b/OpenActive.NET/models/SessionSeries.cs
index 04946ef..669ee44 100644
--- a/OpenActive.NET/models/SessionSeries.cs
+++ b/OpenActive.NET/models/SessionSeries.cs
@@ -70,10 +70,16 @@ public override string ToString()
         [Obsolete("This property is disinherited in this type, and must not be used.", true)]
         public override long? RemainingAttendeeCapacity { get; set; }
 
+        [Obsolete("This property is disinherited in this type, and must not be used.", true)]
+        public override SingleValues<string, DateTimeOffset?> StartDate { get; set; }
+
+        [Obsolete("This property is disinherited in this type, and must not be used.", true)]
+        public override SingleValues<string, DateTimeOffset?> EndDate { get; set; }
+
         /// <summary>
         /// Relates a parent event to a child event. Properties describing the parent event can be assumed to apply to the child, unless otherwise specified. A child event might be a specific instance of an Event within a schedule
         /// </summary>
-        [DataMember(Name = "subEvent", EmitDefaultValue = false, Order = 9)]
+        [DataMember(Name = "subEvent", EmitDefaultValue = false, Order = 11)]
         [JsonConverter(typeof(ValuesConverter))]
         public new virtual List<ScheduledSession> SubEvent { get; set; }
     }
diff --git a/OpenActive.NET/models/Slot.cs b/OpenActive.NET/models/Slot.cs
index 305e987..2ac81f2 100644
--- a/OpenActive.NET/models/Slot.cs
+++ b/OpenActive.NET/models/Slot.cs
@@ -202,7 +202,7 @@ public override string ToString()
         public override string SchedulingNote { get; set; }
 
         /// <summary>
-        /// The start date and time of the slot. Can be specified as a schema:Date or schema:DateTime
+        /// The start date and time of the slot.
         /// </summary>
         /// <example>
         /// <code>
@@ -210,11 +210,11 @@ public override string ToString()
         /// </code>
         /// </example>
         [DataMember(Name = "startDate", EmitDefaultValue = false, Order = 39)]
-        [JsonConverter(typeof(ValuesConverter))]
-        public override SingleValues<string, DateTimeOffset?> StartDate { get; set; }
+        [JsonConverter(typeof(OpenActiveDateTimeOffsetToISO8601DateTimeValuesConverter))]
+        public new virtual DateTimeOffset? StartDate { get; set; }
 
         /// <summary>
-        /// The end date and time of the slot. Can be specified as a schema:Date or schema:DateTime
+        /// The end date and time of the slot.
         /// It is recommended that publishers provide either an schema:endDate or a schema:duration for an slot.
         /// </summary>
         /// <example>
@@ -223,8 +223,8 @@ public override string ToString()
         /// </code>
         /// </example>
         [DataMember(Name = "endDate", EmitDefaultValue = false, Order = 40)]
-        [JsonConverter(typeof(ValuesConverter))]
-        public override SingleValues<string, DateTimeOffset?> EndDate { get; set; }
+        [JsonConverter(typeof(OpenActiveDateTimeOffsetToISO8601DateTimeValuesConverter))]
+        public new virtual DateTimeOffset? EndDate { get; set; }
 
         [Obsolete("This property is disinherited in this type, and must not be used.", true)]
         public override List<Event> SubEvent { get; set; }