@dutchie I’ve done both of these things. My Garmin Vivosmart (with a little OLED display) lets me mark down “going to bed now”. I have used that the next morning to enter in the time.
I did not have weasel problems, but that’s a “your brain” thing. You can enter in data for the previous day, but I don’t ride the edge of the road, so you might lose out on a day of road. Not sure.
Also, I wrote a tutorial on rigging up a wifi beeminder button for the purpose of beeminding bedtime.