has anyone been denied entrance during their grace period.
I saw quite a few groups turned away. One guy was VERY unhappy at Splash Mountain. They might have had to get security. We didnt stick around to find out. 
Is the grace period also 5 minutes before? We got in on a couple 2 or 3 minutes early last week. One person in line in front of us got in 10 minutes early.
We were just at Disney, and I never saw them grant anyone an exception. They were looking VERY closely at the FP. I doubt they will grant very many, if any exceptions, because people are so devious, and can lie with a straight face. We didn't realize they had granted exceptions before, LOL, so we were not impacted, though we did notice the lines for return were much shorter toward the end of day. One couple ahead of us in return line for Soarin' said they weren't happy because they collected them all day, then returned in the evening to ride. I had asked them if they did this after a "big wig" was watching the FP line at Soarin' and they asked if it was true (new rules). He said that it was always meant to be, but somehow got away from it and it was messing up the whole system (agree), but they would now strictly enforce the time window. I thanked him profusely, because our FP line waits were much shorter.
We were just at Disney, and I never saw them grant anyone an exception. They were looking VERY closely at the FP.
I saw quite a few groups turned away. One guy was VERY unhappy at Splash Mountain.
)Do you mean they were later than the end time of the 1-hour window?
Or do you mean they were later than 15 minutes after the end time of the 1-hour window?
I was allowed to use a Rock n Roller Coaster Fast Pass 18 minutes after the end of the 1-hour window on March 22. (Probably because I asked so politely.)
I'm with you, I think some are misunderstanding the OP's question. To me they appear to be asking specifically about the 15-minute grace period.
Do you mean they were later than the end time of the 1-hour window?
Or do you mean they were later than 15 minutes after the end time of the 1-hour window?
In the bottom right-hand corner of the Fast Pass, there is a time printed in very small numbers. This time is always 15 minutes after the end of the 1-hour window.
So I've just assumed that this is the time which the CM actually checks (the print being so small that this may be the reason why CMs were observed to be checking the FP so carefully....).