You can prune the trunk up until you are satisfied with its height any time. I thought you were pruning the canopy changing the overall shape of the tree. In photo #2, it looks like you have 3 or 4 well spaced branches growing up plus some lower growing sideways branches and brush. I would prune up to those 3 or 4 branches. Hopefully they are high enough to give you the trunk you want. If not, wait a couple years to see what grows. Trees have a mind of their own sometimes and those might be the main structure branches this tree plants to produce.
