yah, try to do the heavy pruning as early as possible. The rule of thumb is right after harvest. If you do hard pruning too late in the season, the pruned limbs will be overly vigorous and flush vs flower.
I try to do mine in July, but there still may be time to do a prune now. It depends on a lot of factors though. Some trees (eg, carrie and probably coco cream) will still flower even after a latish hard prune. And, tipping can generally be done fairly late (ie, into sept) without much in the way of ill effect, since there is still time for 1 or 2 flushes before the growing season ends. I've seen some trees even flower out of the tipped ends.
It also depends on climate. Some years the growing season ends in Oct, and in others it will extend out until Dec. So, a prune in Sept could lead to a varying number of flushes before the growing season ends, depending on the climate.
A producing keitt tends to not be overly vigorous for the reason you state -- the fruit hangs on the tree until Sept / Oct, so the tree only gets 1 or 2 growth flushes in before the rainy season ends and growth halts. You'd probably have to keep a more light and consistent approach to pruning the keitt to keep it productive.