I think an hour or so grace period after the time printed would be fair, I can understand why they wouldn't want a 10:00 AM ticket to be used at 9:00 PM, but I think it's going to cause problems for them when they don't let someone use a 10:00 AM ticket at 10:05. However, if this also means they'll stop giving out too many fastpasses for certain attractions (Peter Pan's Flight, for one), I'm all for it.