and if they do, they do. but people who are determined, will beat the system. They'll just get a mgr and give them an earful. Most mgrs have 'bigger fish to fry' then someone being 'off' on their FP return time. They'll just tell the CM to let it go. If I had a buck for every time we saw this situation at Soarin', I could stay at the GF.

Mgr CM says to other CM to 'let it go', not worth the battle.
So it won't get enforced across the board because they're always be exceptions. So why bother if you're going to make the exceptions.
As a matter of fact, we were given FP's because of a ride breakdown, and they couldn't get enough FP'S fast enough so they gave us already expired ones and said they could be used at any other time that day (provided they were able to get the ride up and running again that day, which they did anticipate being the case). So based on that, we wouldn't get to ride because window was already expired and CM's are the ones who gave them out?! That makes great sense.
I anticipate they'll try enforcing it, but it won't be worth the grief they'll get from people. So they'll let it go. Wouldn't be the first time this has happened. There aren't supposed to be any heelies in the parks, but the CM's do a good job of ignoring them as they 'fly' by the CMs (not all, but many more ignore that 'rule' than don't)