Best time? February.
They are very forgiving and you can hack them way back...though, many people call this Crepe murder. The larger the cut, the more likely wood decay can set in.
Proper pruning would be cutting small branches and try to keep them under about an inch. What is proper and what is common practice often get mixed up when people are keeping up with the Joneses.
In a perfect world you'd have a cultivar that's mature size fit the planting location.