Two quick observations... and an opinion.
Our party of six was there for six days in mid July and used a lot of FP and never had any issues or problems with using FP outside the window.
It's kind of funny, I've been on this board just long enough that it seems like this thread comes around about every three months... and it always descends into the same bigger picture discussion.
My opinion, for me personally and my family, if the FP return times were enforced, it would greatly interfere with our ability to move around DL and DCA. It is not at all uncommon for us to move from one side of a park to the other, or from one park to the other, all while an FP is "ripening". It's actually very uncommon for us to collect an FP and end up using it in the original window, because we usually find ourselves moving around to other parts of DLR. Long story short, if they simply started enforcing FP return times, it would make DLR vacations into a logistical nightmare with constant checking of watches, and calibrations of how long it takes to walk from one area to another -- and honestly, I just don't think it would improve the average visitors experience all that much, maybe, just maybe, it might mean a 10 minute shorter FP return line late in the day, that's about all the advantage that would happen from enforcing return FP times.