First of all, in order to revert to veg, it takes a few weeks IIRC even under 24/7. The lengthening days are unliikely to revert it, and if they do it won't happen on a timescale that is meaningful to you (it will take forever). If you want a larger plant, get it under some CFLs or fluoro tubes to send it back to veg, then put it back outdoors when you are ready to flower it. Keep in mind that when you make the transition back outdoors you should do it gradually (harden if off) so as to minimize the shock of the plant.
In my opinion, however, if you have more seed or a source of clones, you should just leave this guy outside to get a feel for the grow and the satisfaction of the harvest, and start anew with new seeds under at least 18/6 light. It will take so long to send that plant back to veg that it just won't be worth it.
As for the pot, it is plenty big for the size of that plant. It looks like 2-3 gallon clay. I don't go any larger than 3 gallon personally, but I don't grow trees.
cc