It should gain roughly half an inch trunk thickness per year of growing in a flower pot. This one grew from seed, is about 3 years old and it’s about 1.5 inches at the base of the trunk. If you’d like to put it back into that green bonsai pot I’d say a year would be good. The flip side is you will need to prune roots to fit in back into a small pot, the timing must be right, before spring and be careful not to cut too much root as it can stress the tree.