Depends on how many you take. You can easily pull clones from a plant before or even just after you flip them to 12/12. If you are stripping that girl down, you will want to let it recover a bit, but if you are only taking a handful of cuttings from an already bushy mom, you could flip any time. If you are removing 25% of the branches for clones, you will want to give it some time to recover.