On the Iron Dragon, we tried (didn't always succeed, but we tried) to rotate every 20 minutes, and then shifts just flew by! The rotation helps more than I ever would have thought. Plus, then you get to have more opportunities to work controls and every other position, so you're never stuck for so long at each single location.
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PO!NT OF VIEW - A Different Look at Roller Coasters
http://www.crosswinds.net/~justmayntz/thrills/