Finally a sane person I can relate to!

All of the mechanisms others are describing I totally get, but I can never maintain a routine/habit like that after it stops being new - I use various things others mentioned but then after a while & very abruptly/instantly I completely erase most associations with that not-yet-habit.

Eg I have some medicine I have to take daily and in order to take it most days I must keep changing the not-really-habit to keep it fresh - in this case I keep moving where (in the open) I keep the pills every few weeks (or when I casually notice I forgot to take them for like 5 days).

I do indulge myself with variable sleep schedule a lot, trying to manage that (for decades) was not worth the stress (and even much less the benefits of trying to fit in with neurotypical folk). Same with food - if I don't feel like eating for a day I just don't, and when I'm hungry I absolutely try to eat whatever I want bcs that's usually actually very healthy/nutritious food I want. But for both these things I'm lucky my situation allows me to do so.

That thing about eating 3 (or even 5) meals a day is just corporate (industrial) propaganda to maintain fixed schedules in the factories, it's less than 200 years old. In some medical cases (eg type 1 diabetes, liver issues, etc) sure, but Im also sure that, like with exercise, you get some endorphins when your liver goes to work into the opposite direction bcs you depleted short-term energy reserves (various carbohydrates in blood and liver?).