Mon-Wed nights work best for me, 5pm PST ’til whenever.
All other times are subject to wife approval, so probably <10% of the time and only with advanced notice.
If I recall correctly, one of the videos about raids (DevSpeak maybe?) said that raids would be pretty long (GA, ~4 hours; DS ~6 hours). I haven’t heard anything about leaving a raid and coming back (e.g. the next day) to continue where you left off, but I imagine they will need something like that.