Depending where you are it could be as early as this summer. I would look for roots coming out the drain holes as an indicator. If you don't do it this summer then I recommend you up pot at the start of next season. Probably a 2 gallon container should work for a year or two (again depending where you are).

Jungle Jacks recommends waiting until Mid-July to repot the ones you buy from them in the big box stores. I got several of theirs from Lowes 1 month ago, that I'm planning to repot next month. That should give them enough time to beef up their root system in the little beginner pots they sell them in.