how fast do you want your tree to grow? i keep mine in 1 gal for a yr or longer. when i move up, i do extensive root work. since they are in 1:1 perlite and seedling soil, it's easy to do this.
however, this also means my trees are growing very slow. first 3 trees i started with were up potted very fast. 1 gal to 3 gal in 2 months. 3 gal to 10 gal in another 4 months. by fall i had enough growth for cuttings.