Oh incidentally I learned recently that things you learn in the last 90 minutes or so before going to sleep are less likely to be retained.

I believe I read this in "The Expert's Guide to Sleeping Well" by Chris Idzikowski, which is a well-researched book... but I didn't take any notes on where in particular I read it.

It was a striking result because a lot of research shows that sleeping after studying is crucial to consolidate the learning -- this added the nuance that a gap between the study and the sleep is also needed.