There is a booth outside the rides where they'll actually give you a handstamp with the specific time to return and ride. The only problem I found with the system was by the end of the day when it came time to ride, I no longer had a legible stamp, but more of a smudged, faded, reddish area, that looked like some freak rash ;)
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-FCR
I'd Rather Be Riding Roller Coasters