How reliable are crowd calendars?

[WDW in Pearls]

Hi everyone!

I'm a bit of a control freak when it comes to Disney trips and like to plan my park time to the hour! I'm not opposed to adjusting as needed but I'd like to at least start on the right track.

I've started looking at crowd calendars from various sites and was wondering how reliable others have found them to be? Any sites in particular that are especially good/bad? How far out can you typically get an accurate prediction? Thanks everyone!