~72 hours. I think I went beyond that, but gave up because there’s diminishing returns for fasting that long, that is, your body starts shutting down in a way that eating again after that period can be dangerous if not done very slowly with like bone broth or whatever.
Mind you, it’s not easy fasting what with it being impossible not to flush out electrolytes, so making sure you get enough salt, magnesium and potassium supplements is a must. Obviously, other vitamin supplements doesn’t hurt. The only dangerous one is potassium, so make sure the dosage is right. Oh, and there ought to be enough calcium in the tablets alone if you take vitamins daily and depending on where you live, if the water is hard enough (like here in Denmark), that’s another source.

I was already on Mastodon by just having a Vivaldi (the chromium browser) account, and it’s just lovely I’ve spent most of the day setting up lemmy, even though I joined feddit.dk 2 years ago, it’s only just now I’m taking it seriously.
And, while not related to the fediverse per se, I switched to linux a year ago.
The only service that’s hard to drop/switch away from is Youtube imo.