I've read that in cave studies when isolated from any direct indication of time people will naturally sleep longer every other day like this. However, I have severe sleep issues that leave me disabled and the main issue seems to be that I have a non-24 hour circadian rhythm and can't sleep outside the rotating times but in some ways my body is still synchronized to the sun (I do much worse when awake at night). So I worry you could also potentially end up with severe circadian issues unless you are completely blind, although if you always wake up at the same time whenever you do sleep that would hopefully help prevent issues. Sleeping in late some days makes circadian issues more likely.

Taking more than 20 minutes to get to sleep is not that unusual as I understand it. I think 30 minutes minutes is quite common even in people who sleep fine. 4-5 hours is very short though. One of my parents also slept little and there is also dementia on that side of the family (I have some memory issues as well already). I don't know how much previous gnerations slept but I suspect there may be not so benign genetic short sleep issues as well. At least some issues may have susceptibility and a triggering event, with tech making the triggering event more likely. That would be another question about benign familial short sleep, if it increases the susceptibility to more severe issues.