MWC was a Sep 1 deadline when BYU announced their departure...
That could have changed now but I've never seen any official info to support that.
AAC as others have said is a 27 month notification if they are to depart without financial penalty. Anything less will have a large penalty (the shorter the notice the higher the penalty) what ever penalty is sought by the AAC will be arbitrated for a final amount both sides agree upon (likely less than what is asked for). Note that I believe Louisville paid $11M to the Big East/AAC. They announced toward the end of November 2012 and they started in the ACC on July 1, 2014 which was just barely over 19 months from announcement to official start.