Pretty simple, since the dungeon/missions/dailies count resets and allow you to do more of them at 6am EST; You should consider waiting until that time before performing any Scheduled, or “Temporary” maintenances.
By having them right before the maintenance, some who procrastinate too long will lose out on a possible day’s worth of dungeon runs.
(Especially when one doesn’t know about a non-scheduled maintenance, then the dungeon finder doesn’t pick a party for 10~20 minutes at a time while you try to scramble for last minute dungeon completions)