personally I would wait unless the strain is known to stretch a lot...and then I would flower short clones...i think the maturity from seed time is important...having said that...i have flowered early...seemed like the effects didn't last as long ...just my .02 cents
If they're clones you are good to switch em when you want. Depending on when the cuts were taken the clones are the same age as the mother , should have pre-sex hairs at the nodes already.