I stayed at the Grand Floridian for Goofy in 2013 and took detailed notes on my phone the morning of the half, so that I would know what to do the next day for the marathon...
I arrived at the monorail station at 3:28AM. A monorail was there waiting.
We arrived at the TTC at 3:36AM.
I was on a monorail to Epcot by 3:39AM.
I was at the Epcot monorail station by 3:50AM.
From here I made a stop at the bathroom near the monorail station (one of the last opportunities for a real bathroom before the race began) and made the walk to the staging area. I think the bathroom/walking took about 20 minutes.
So that gives you an idea of the timing. The above scenario was with no monorail stops or whatever.
We all know that the wake-ups are a part of these races. They suck and I totally understand wanting more sleep but you never know what'll happen. Maybe it's the rule-follower in me but I wouldn't risk being late to get a bit of extra sleep.