Flanker,
Funny, I was bidding schedules at a commuter airline with 20 airplanes 20 years ago. Some bidding systems close the Captains bid the day before the F/O bid so as to allow the F/O's to bid around problematic Captains. Not only do we bid monthly schedules but we get two more opportunities to bid after the first bid is closed before our schedule is official. After this point your schedule is variable; as any extra time that becomes available durring the month can traded with.