I have a couple California live oaks seedlings and Quercus suber Cork oak seedlings. I do grow in a climate too cold for too long for these oaks to survive outdoors for any length of time in winter. Therefore I winter them in a near freezing cold room, a dis-used well house that is underneath my patio, and accessed through a trap door in my basement foundation wall. Entirely below grade, hovers about 35 to 38 F even in -10 F weather. And stays below 38 F even on the days that jump into the 50's during our short 2 or 3 day February thaws. So it is a nice even temperature. But it is dark.
After a few months in dormancy I bring them into my light garden, then out in the yard after last frost.
With my climate in mind, Ted Matson recommended only working on the live oaks and Cork oak in early summer, while everything was in active growth. This is a tree where all defoliation, pruning and repotting are done on a single day, for me early June, then just let the tree grow until the following june. Of course wiring and other less disruptive tasks can be done anytime, but the pruning, repotting and defoliation should only be done while the tree is in active growth.
That was his advice, I'm in year 5 with these, and his advice has worked for me.
You are in California, so timing and perhaps the tree's tolerance of disruption may be different. Your climate is different.