Is it possible to get a per-notebook running time from myst-nb?

[billbrod]

Hi all, I've been playing around with myst-nb and the sphinx-book-theme and really enjoying them, thanks for all your work! I was wondering if it's possible to get a line with the per-notebook running time at the bottom of each notebook, similar to sphinx-gallery or mkdocs-gallery.

I see the nb-exec-table directive, but that contains too much information; I just want the running time, and I want it displayed on each page. I don't think I can edit the output of that directive, right? And while that info is stored in a sphinx environment object, I think I would need to write a sphinx extension in order to access it? I was hoping for the ability to write a template that I could insert into the footer or something similar. Is there an ability to do this or something similar?