2 yr old Japanese Maple Seedling

I recently bought a 2 year old Japanese Maple seedling that is approximately 30 inches tall and is about as thick as a pencil. It's in the same 4 inch tall narrow container that I suspect it was germinated in. My question is, is it okay to transfer it to a 4 inch net pot and trim the tap root (providing there are enough fibrous roots) at this time of year in San Diego, Ca.? I am in zone 10a. Or should I wait until Fall?

No, best time to repot maples is by late winter / early spring, right before they sprout...

I'm thinking that maybe that pot you're talking about is too small?
It's good if it can have more volume, but wider, not deeper.

I generally go from pots about 1L (for seedlings or cuttings) to 3L pots (which is almost a gallon)...
then for 5, 8  or even 10 Liters depending on how big I want to grow it.
 

Albas,
Just to clarify. It's okay to repot it now as long as I put it in a net pot that is wider but not deeper and leave the roots alone? I was wrong about the current container, It is currently in a pot that is 3" wide and 5.5" deep. And it has some roots growing out of the holes at the bottom. So I do feel it's current pot is too small. I have two different sized net pots, one is 4" wide and 5" deep and the other one is 8" wide and 5" deep. Or do you mean to leave it alone until late winter/early spring? 
As far as the size of the tree goes, I'm was thinking about 2 to 3 feet tall when it's all said and done.

I don't think it's a good idea to do rootwork in maples during summer, that will probably lead to hydric stress and the plant will spend a fair amount of it's energy to recover, instead of using that energy to pass healthy tru' it's dormancy...
Even if you just slide it to a new container, you'll still have to work on the roots in the next window, so just wait for now, and do the full repot / rootwork then...
Wait for late winter/early spring, and do all  the rootwork that has to be done then, it will be waaay safer...


A 2 to 3 feet tall tree is quite big, it will be much harder to make it on pots, big sized tree's are grown in the ground in most of the cases...
What you can do once it drops it's leaves is to wire the trunk and give it some movement according to the design and size you want, smaller trees = tighter curves, bigger trees = smoother curves.

Thank you Albas. I really appreciate your time and your guidance.