You can force, essentially, MJ to flower at anytime by going to 12/12...

Even plants just 2 weeks old will force flower.

However, if you choose to then take the forced sexed flowering plant BACK to veg state, it is said you can turn a plant hermi...although I have never seen or done this.

So, if you have smaller plants under 12/12 now along with your big ones, both are in flower state.....