Hi friend!
Im experimenting a technique since 1.5 years now on my tree.
I decided to experiement in bulding a canopy on a ficus starting from the 6 main trunks and a great total of 12 branchelets the size of a toothpick..... ( I know 6 trunks is politically incorrect but there's a whole story behind it.. my tree my choice!),
Still to put it in my own way, I don't often see examples of ficuss that have a well-developed secondary and tertiary branching here in my corner of the globe.
Maybe is just that I dont attend shows enough but they are mainly abscent in developped forms and Ive seen what theses trees are capable of.
Without really knowing what I was doing I started trying different techniques using different timing. And I think I arrived at an interesting method that allowed me to build this entire canopy in 1.5 years in the northern hemisphere.
I really dont want to share previous pictures of this tree as it would show my complete lack of knowledge, but I can assure you its a complete ressurection and there's way more to come.
@sorce, in his own way of course

Has already given the answer to this great question in his post above timing is the only thing that's important, not much the time of the year, the entire tree yes for its general health but the current state of the branche you're working on and not the one aside.
Keep in mind, more branches equal more energy spent by the tree to build the canopy, which will RESULT in shorter internode lenght and smaller leaves on the newest branches and if lucky on the existing secondary branches.
See this link for the detail on the timing and method I use on my tree
https://www.bonsainut.com/threads/backbudding-on-ficus.55788/post-965351
There's lots of work to come for this tree to improve alot of things but as its my first tree I want to improve it as much as Im capable of and so far it respond fairly well.
Hope that help
Ugo