For SKW monthly schedules, bidding opens on the 11th, closes on 17th, awards are out by the 19th, and final schedules are out on the 24th.
It's possible, but very unlikely, for there to be a change between your award and your final schedule. So basically we know by the 20th what the next month will be. We can start adding/dropping on the 24th.
Mesa did a rolling 28 day bid, so there were never fixed monthly dates, but the lead time was similar.