This has been gone over on the Theme Parks board, because as of this month, Disney is strictly enforcing the Fastpass return window. The Fastpass time you get is going to depend entirely on when you pick up the fastpass and how many have been distributed ahead of you. So there's no real way to know what the time on your fastpass will be before you get to the fastpass distribution point.
If you get there and the time for current Fastpasses will fall during your ADR time, you'll be deciding whether to get the Fastpasses or go to the meal, and with CRT you'll probably choose the meal if you don't want to be charged for it. Might be better to try going back later to see if you can get a later Fastpass.
As for the "what if my meal runs over time and I miss my Fastpass window" we also don't know whether you get to use the Fastpass anyway. You would probably have to go to Guest Services and see what they could do, because it appears Disney is serious about enforcing the time limit on the Fastpasses.
