3 Hours actually...I guess they like to make the Monday daily shortened which suck for me as I only get 3 opportunities to do dailies over the course of the day. 2 Hours after the change over (Just before bed), then on my lunch hour during work and lastly after work, but on Monday's by the time I get home they are already doing maintenance.
I guess it may be just a set time that is used for all maintenance whether they are adding content or not. That way if anything goes wrong during the update they still have time to correct and fix it and I guess the same could be said when removing events, things can still go wrong thus why the maintenance time may be so long.
But without actual insight to the devs routine I can only speculate.