Not to be mean but this topic has been dicussed over and over ad nauseum.
the fastpasses have a starting time and an ending time....in other words a window.
If everyone uses them outside the window, then the fastpass idea collapses and the process becomes slowpass.
I have been turned away with an expired time fastpass and it was most embarrassing for our family, however I have heard about folks using a pass when it was a few minutes late as well.
It really comes down to folks thinking about the process and striving to behave responsibly....when rides are broken the CMs will usually tell you they will honor expired passes, other than that you know the answer, it is your subject line "EXPIRED fastpasses.
Now for everyone that is dying to chime in here and tell me and the OP how you've used passes from 9AM at 8PM in the evening and gotten away with it and even better a CM told you "use them anytime you want"...great you beat the system, but you know as does everyone else does.
If they designed the fastpass to not have a window they would only print a starting time, not an ending or expiration time! Period.