I have spent about 15 years without maintaining a sleep schedule, since otherwise I had trouble getting to sleep in the evening, had trouble waking up in the morning, and it is nice to study, work, and be awake in general in night silence, occasionally observing the sky at dawn or dusk. Yet most people being awake during the day and assuming that everyone is makes it inconvenient, as does simply the increased difficulty of making plans with others (sleep-wake cycle lengths were perhaps around 25 hours on average, but variable for me). Since 2020 I am trying to keep a schedule again, and here are notes on issues (and occasional solutions) arising with or without a schedule.
Among other things written on the topic, there is the "Sleep regularity and major adverse cardiovascular events: a device-based prospective study in 72 269 UK adults" study, and a humorous Initiative for the Prolongation of Earth Days to 30 Hours.
In Moscow (UTC+03:00, latitude 55 N, longitude 37 E) days (from sunrise to sunset) vary between 7 hours (9 to 16) in the winter and 17.5 hours (03:45 to 21:15) in the summer. Dawn and dusk last for about an hour each, nice plots are available online (e.g., sunrise and sunset times in Moscow). People walk their barking dogs until midnight, and for a couple more hours (until 02:00, though sometimes even 03:00, especially on Fridays) kids, drunkards, and hobos make noises. At 4 to 6 o'clock outside noises resume, with garbage collection, street cleaning, construction works, and similar activities. Most birds begin chirping at sunrise.
Common working hours are from 9 to 18, grocery stores and cafes are commonly open from 8--11 to 22--23.
Unfortunately 8 hours of sleep don't fit into silent and dark times (except for rainy days, and possibly winter ones). But it seems useful to adjust the regime to slight changes, such as waking up on sunrise instead of a fixed time. Even failing to sleep sufficiently long in one go, one may try to compensate for it with naps. I find it helpful for better/uninterrupted sleep to not force sleeping while not being sleepy, though that's tricky to combine with 24-hour days.
Good shades can block undesirable light sufficiently to avoid waking up due to light even on a sunny day, though light is very helpful for maintaining a schedule (particularly if sunrise happens at a reasonable conventional time). Double-paned windows provide good acoustic insulation, though closing them reduces the air flow. Thick walls and appropriate doors help as well. Active noise cancellation seems fun, but apparently of limited usefulness and challenging to set.
Music is nice to leave on while sleeping: noises are easier to notice (and to wake up because of them) in silence, and it's a handy indication of the computer working fine.
Some suggest to generate white noise to achieve a similar effect (drowning
other noises in it). One may also generate more natural (sea/rain-like)
pink or brown noise with play -n synth brownnoise synth pinknoise
mix synth sine amod 0.3 60.
There's "weak and inconclusive" evidence that sleep hygiene works, but apparently it's not recommended anymore in 2021. Even though some of the practices proposed under that label seem sensible, and appear to match my observations (e.g., naps and worrying potentially harming night sleep).
Sedatives come with unpleasant side effects for me, though seem to work much better for others. Apparently some find melatonin-based medication helpful, but perhaps it's better to consult a doctor for those (prescription is usually needed for any working/non-placebo medications of that kind anyway).
Work is common and commonly time-sensitive. Even programming, though easily asynchronous and remote, is often required to be done at certain times of day (usually conventional working hours) and/or in certain locations (usually an office). So the requirement for it to be remote and flexible limits options on job search, making it particularly hard if you're also picky about tasks (e.g., want to do something at least remotely useful or harmless), technologies (especially if you prefer uncommon or less hyped ones), or salary. Once a suitable job is found though, the workflow can be quite similar to working on FLOSS projects: mostly over email, possibly with use of IMs and issue trackers, occasional meetings. It's even suitable for operations (server maintenance), not just programming.
I have never found voice conferences to be useful for work, but some like those too. Or even video conferences.
I tried to avoid excitement of my regular hobby activities, including software development and maths studies, since I knew that it can easily interfere with sleep, as well as with daily routines that seem to assist sleep, physical exercises in particular. And indeed, even 3 years into maintaining the sleeping regime, and about a year into having an exercising routine, I started working on a hobby project more actively, which led to increasingly disrupted sleep: once again it was hard to fall asleep, to keep sleeping, to wake up on time, and the daytime activities were less orderly then, just after a few days of relative excitement. It is not great to give up on fun and excitement, but giving up on sleep is pretty bad, too; as a compromise, one may try to manage it.
Later I noticed that while falling behind on a schedule due to unplanned naps, I hurry to catch up on physical exercises, work, other daily plans, then having a hard time falling asleep, which leads to lack of sleep, and more of those unplanned naps (which would simply be oversleeping if I did not use an alarm clock), more hurrying and stress. A seemingly appropriate strategy for dealing with such situations, which I am trying out, is to attempt to calm down intentionally, maybe add some meditation and calm reading into the daily schedule, but cut on other unnecessary activities, try to relax about things like work, maybe put some of the stressful activities on pause. Perhaps replacing a strict schedule with doing as much as you can comfortably, yet without procrastination, so that it would still be the best (comfortable) effort, and will not feel like slacking.
A related observation is that simply shifting scheduled activities forward or backward in time, while those activities taking the same amount of time, may lead to either being late with (and stressed about) everything, or completing them all early. Which makes it more important to both schedule appropriately and avoid delays at the beginning.