Took a closer look at what I could see of the line setup, and I think the overflow block would only hold about 45 minutes, if that, without Express. Given that this will be a new ride with Express from the start...I'd hedge on doubling that if you get in line at the wrong time. Also, you can tell that they don't intend for that block to be there all too long for every day use by how they have the rails set up and put into the ground. Very smart, as its easier and looks a lot nicer than having to go in later and re-weld and rip up and patch concrete/asphalt. If it weren't for Express being used, I would actually say the overflow block is fine as it is, lack of shade and all. Also, the building keeps growing on me, and I really can't wait to see Optimus over the entrance area.
As for when its "officially" opening...I know someone who would be able to give me as concrete an answer as you can possibly get, but I rarely see them, maybe once every two months. I expect I'll know when they intend to do softs as soon as a day or two before, though. I'll definitely keep my ears open and info flowing if I get it.