Growing New JM Leader After Chop - When To Prune Back

[Firstflush]

I’ve posted this tree already. The leaders are plus another 6-8 inches. It has been growing untouched for about 6 months. Chopped last fall early winter and repotted early spring. Can it be pruned back or should I let it go until dormancy and it drops its leaves?

 

[Forsoothe!]

It needs to grow, leave it alone until it loses its leaves.

 

[Shibui]

Maples can be pruned any time of year but whether to prune depends on your objective.
After a trunk chop the new leader needs to grow enough to become well attached to the trunk and to get thick enough to start to blend in with the original trunk. I find that can often take a few years so don't be in too much of a hurry to cut again.
Any developing branches can be pruned to reduce their strength - don't want branches as thick as the trunk - and pruning these will start to develop ramification.
Bonsai takes time. Good bonsai takes even longer.