generally as far as i reckon, if the tree is a slow growing species, to leave it in the ground or grow box/pot until the nebari/trunk/main branching is sorted and you are happy with it. then it can go to an "oversized" bonsai pot, and the finer development can be finished of in that, then once complete it goes into the pot you would like the final size to be.
faster growing species, i generally keep in the ground/grow box until trunk/nebari and some main branches are the right thickness, then do the same as above.
the longer you can keep it in the grow box/ ground the quicker the development of the tree.
i suggest you read some articles on ground growing and growing for taper as these will enlighten you on what you should do
taking the top half of trees of since 2005! 
