Riots usually happen around Day 30-ish, and they will last about 5 Days. Make sure to check on Annalie, Shanice, PriestBot, and Hobo during the riot. But if you don't care about them, you could just sleep it off for 5 Days, nothing too crucial will happen to them even when you're not visiting them at all during the riot.
For the requirement for it to trigger... I really do not know...