Keeping to the 'week of waking before the alarm', I shaved a massive 35 minutes off this morning. Not quite sure why; though as I'm not currently feeling any negative effects I'm not overly concerned. Will see if things change later in the day.
Following nap
That was an interesting test. Tonight I was out until around 21:30 - around 2 hours later than my usual nap start time. As expected, I found myself dead on my feet by the end. However, afterwards I had perhaps a 40-50 minute nap, which seemed to reset things a bit. I guess I'll find out tomorrow whether that's enough, but I shouldn't imagine the occasional shorter nap will do any harm at all.