Most places suggest you prune after harvest.
Since this is a young tree, I will time it by when (your) older trees of the same variety fruit (in the area you are in.
In my part of south FL season ends mostly by October and that (early October) would be the latest I will suggest. To be certain, leave a few tips uncut. If it is too late, at least these uncut tips may flower.
Others with more experience can please chime in.