If we really, absolutely want to make rope drop, then we leave 1 hour and 15 minutes before park opening. We've "just missed" a monorail before and waited 10-15 minutes for the next one. Situations like that are when the extra 15 minutes is the difference between making rope drop or not. Of course, if everything goes as smooth as possible, you may have 30 minutes to wait once you get there. I will say that we're always stuck at busy travel times like Spring Break, July, Thanksgiving, or XMAS, so I have no experience with less crowded times!