We're doing tandem drop panels as well in our first scare room. They are about two feet apart and are actor operated. Another actor in the main room will give an audio cue to the DP operators to release the latches. They will drop at the same time, and when they hit perfectly, give a loud slam and a great scare. I think having them out of sync will diminish the second scare to a degree. Our actors will be doing a three count to each other to coordinate the release so that may be something to consider if your actors are close enough to each other.