How long is the repot window for a Chinese elm? It is really early, but mine has already started producing new leaves? Is it too late?

With the right aftercare you can repot a lot of plants for a large part of the year. Inwould not be worries about repotting after buds have briken, naturally partially depending on the amount of rootwork you are anticipating.

It has gotten cold here again.. with below freezing temps. would there be any issue there? I have the tree on a balkony, that, even when is below freezing stays a bit warmer.