There are so many factors involved, I think it's hard to predict a general time of day like that. Weather, other rides (say, if MF is broken for the day or whatever), general crowd size, setups, etc... Later at night, like just shortly before the park is closing, the line seemed to go down, but it really depends more on when in the summer you're there - June and August are very different! I've seen Raptor at practically every hour of the day full one day (1+ hour wait) to 15 minutes the next. My best suggestion: just keep an eye on it, and if the queues are getting empty, go for it! :)
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PO!NT OF VIEW - A Different Look at Roller Coasters
http://www.crosswinds.net/~justmayntz/thrills/