Yes, split as the main flow is ending. This is what I would do. It will be about a month before the new queens are laying. In Delaware July and August are really slow nectare times. By splitting now the bee population per hive adjusts more quickly to the dearth conditions, and is well prepared for the fall increase in nectar. Also splitting now reduces the mite load for the new hives.
I did splits last week. The new hives are building comb and laying in nectar. Looking good so far.