I like the idea of users being able to pick their 3-hour window and timezone, and maybe only can change your window setting once per day (or maybe only pick a new window that starts at least 24 hours in the future). But crucially, each such 3-hour window and time zone combination has entirely isolated and independent content, as if it is a different site.

So my community could be 7:02-10:02pm EST. And if I instead switch to say 6am-9am IST instead, I can check in with the folks who like to meet in the mornings in india, but I am temporarily gone from my own local community.