September not a busy time. Like others have said, be there at rope drop, walk straight there around the right side of the Castle, walk right on with maybe 10 minute wait. Note that rope drop has typically been around 8:45am instead of the published 9am. On a different day, we got out of Crystal Palace at 8:55am, didn't realize park opened 8:45am. We were behind a lot of people. The line was long, but it moved pretty quick, waited about 25 minutes. There were some people returning with FP just after rope drop, but not many.
Also like others said, we had great luck one night right before park close. Posted standby 40, but just looking at the line you could tell that was way off. We got in line 10 minutes before park close, waited 10 minutes. There was no one returning with FP at that point.