In all of them I've seen it's a window that starts when you haven't been using it in a while and begin work OR when your previous window expired. The window starts with a set number of tokens and cuts you off when they're used, it is fully reset at the end of the window (it's not a sliding window).
When you haven't used any tokens for an extended amount of time it reverts to the point where whenever you send your first token is when the window begins.
Hm, it seems like it'd make sense to automate a script to send one small prompt at, say, 7 or 8am so that you get your reset around noon instead of having to wait until 5h or more into the workday.
I never quite understood why they picked 5h, it seems oddly arbitrary
When you haven't used any tokens for an extended amount of time it reverts to the point where whenever you send your first token is when the window begins.