Agree that April/May is a good time, because the closing then happens right after school ends and people can move in during summer vacation. It also depends on your climate, we have no snow in my area, so things don't really shut down in winter. My town is top rated for schools, so most activity matches with closings during summer vacation.

In cases like yours, where the deal fell through due to buyers and not because the house had issues, I've seen realtors add the following sentence to the top of the listing when it was relisted ...
"Back on market due to buyer financing issues"
"Back on market due to no fault of the home"

Buyers will assume that the house has a problem and the realtors are making sure they know it was the buyers that had the problem.