I doubt they're really enforcing the "after window" time on the ticket, as long as you're not early. We went in October and had no problems if we were a little bit late getting there. I think maybe their philosphy is that there are only so many FP's that are distributed daily, and it won't make a difference if people are late getting back to the ride. It may make for a crunch for the FP holders if they all decide to come back at the same time. However, it makes sense to enforce the beginning of the time window. If they didn't do that, people would just get FP's, then go right in the FP line. People would see how that's done, and then clog up the FP lines, making the reward not worth the effort.