I prune mine lightly any time a branch is irritating me, but I feel the best time to prune is mid-to-late winter, say December-March. My largest maple is still holding on to a few leaves, so I'll wait before I give it a slight haircut.

Good luck!
Grant

I love the open airy way they have them pruned at the Chinese and Japanese Gardens but can't seem to get that in my yard.. My Atropurpuream (sp) is really dense and casts too much shade but no matter how much I thin it it still grows that way....

Pruning the interior lightly is fine for most trees all year.

If there is a "perfect" time, it's after the leaves fall and after the leaves appear.

So wrote Dr. Alex Shigo, said by many to be like the "father of modern arboriculture".

But he also wrote that pruning can be done all year.

"Perfect" implies perfect in the sense that there may also be a "perfect" temperature at which to wash your car, or a "perfect" number of hours to sleep each night.

I feel that dormant pruning is excellent for novices so they can see the branch structure easier.

Spring pruning is fine too. The supposed maple "bleeding" fear is on the verge of a myth.

That was one aspect I made sure to ellaborate on in my own site's pruning basics page.

For now, you are good to go, but no crisis if you don't get to it until May.