You should wait for a healthy and vigorously growing plant, if doing it early as possible. 6-7 nodes will be safe and not kill it, assuming you aren't taking off 3-4 nodes, lol. When i worked in a greenhouse, they said it's safe to prune every other node, but that wasn't marijuana.
fimming is topping. No 'extra' nodes are ever produced with you top. fimming is a myth, just top normally. If you try to "fim" the best you get is a normal top and the worst is some mutilated leaves that won't cause and meaningful redistribution of auxin.
I'd wait for at least soem auxiliary growth -- and growth that matters, not something tha twill be covered up... If this is a short vege plant, then do it early. If you are growing out a 3x3 canopy, these lower branches are likely to be trash anyway. You still need to top, but maybe not to grow out the lowest 2 for sure.