I have a mimosa and I have to prune it. I'd like to be less invasive and do this "operation" in the best way.
Which is the best weather to prune mimosa?
Which is the best time to do it?
I've decided to give you the information anyway, and you can interpret it for wherever you are in the world in terms of your spring/flowering times. Usual pruning time for this plant (Acacia dealbata) is immediately after flowering is over, when you remove any dead or diseased wood, thin out crossing branches/stems and reduce the size - you can take off two thirds of the growth if necessary.
UPDATED RESPONSE: I don't know whether you get very low temperatures where you are - the risk with pruning now is that you may induce new growth on the plant, which you really don't want before winter arrives, it won't have time to harden off. What you can do, though, is top any long branches to reduce windrock - this is best done when the weather is very cool, so if you can wait till end of November, that would probably be better,on the assumption it's colder then and a greater degree of dormancy is present in the plant. And make a resolution to give it a good prune and reshaping, taking out crossing/twisted stems, next spring after flowering.