Cloning a plant during flowering

I was wondering if it was any waste of a branch off one of my females to try and clone it after it has been under 12/12 for two weeks.

Yes you can. It would be a good idea to flush it for a couple of days first to lower the nitrogen content which impedes early root development. You should trim off the bottom 1/3 of your plants anyway so it is a good time to get some clones. VV

Two weeks into bloom is probably your last chance to take clones. Any longer, and they will take forever to root.