Sorry, forgot to make my explanation #khaneproof.
The base mission time of the elite challenge missions is always 3 days. If you don't properly counter the additional duration events, it's possible for the mission to be as long as 12 days.
I haven't mathed it out, but I'm thinking an 8 champion roster (8th having a -50% mission duration - or however low you can get it) would be ideal now. You'd obviously have to swap out champs 7 and 8 when the command center is up. On my main I swapped my bodyguard/OH/Gold follower with a reduced duration follower since I can get such the AP reward (currently 11.9 mil) challenge mission 3 times. When the servers come back up, I'm gonna see if I can get the mission duration to less than a day.