You can wait until you see the new growth if you want to. How old are these Clematis? ALL Clematis benefit from being pruned as 3s the first few years. You won't hurt 2s to prune as 3s.

for 3s you want to prune just above the lowest new growth or you can just whack them off at a foot tall which is what I do. They sprout out from the vines and up from the crown.

Thank you for the information. That does help. Most of mine are 2 - 3 years old. I have Roogchi, Claire De Lune, Crispa, Multi Blue, Petit Faucun, HF Young. I also have Henryi and it is about 5 years old.

If you did not prune them as 3s at first you can do so now to encourage more vines. 2s tend to get scraggly left on their own. Rooguchi and Petit Faucon are 3s anyway. It took Petit Faucon five years to get going for me but it is WOW now.