The traditional time to prune is while the tree is dormant/leafless, in part because the structure of the tree is easier to see. But major regrowth will occur the following year.

Or one can summer-prune, doing so by early August. This tends to restrain the regrowth a bit the following season.

Overall, you can prune just about any time the pruners are in your hand and you have time.

Due to pears' overwhelming response to winter pruning by pushing out vigorous, skyrocketing, vertical shoots, I strongly recommend summer pruning.