as it is in a pot you can repot it at any time that suits you. But if it has fruits wait until they are harvested. i'd be tempted to do it in the early autumn when the leaves are fading but the roots are still active, giving it a chance to settle down.

I would do it in early fall, also. If it is really pot bound, you may have to do some surgery on the roots to keep the tree from strangling itself, and it will recover from shock faster then.