Generally (not always but generally) the line is not that long at closing time. From my 8 years experience working at WDW in attractions I can tell you, as long as you are in line before closing time you will be able to ride. They will close the line off at closing time (by their watch remember CM's work on Mickey time ) and everyone that is in line will be able to ride, regardless of how many people are there (again right at closing time it usually is not that long of a line). My suggestion is to make sure you are there at least 5 minutes before closing