When is it too late to Fim

I just put my plants into flower. Is it too late to fimm them? When should plants be fimmed?

Plants in general should be trained and topped a week or two before starting flowering. I wouldn’t focus too much on the whole “FIM” idea, it is not very reliable or predictable. Most people end up preferring the regular topping instead of trying to “miss” intentionally.

You can pinch/fim a top right after putting a plant into flower for some interesting double buds, or very rarely a weird triple or more spreading out bud. But this will not increase yeild, all the numerous bud tops will very likely be smaller than the one big bud that would normally form there.