When do I change light time to 12/12?

Is it when the sex's show up,like a female.That's when I change the light's or I can change the lights when I want to for height reason's I read about.Well want my plant to be short and busy,I think it's a Indica plant.Well got the seeds from a dime bag I bought.It's been 11 day's so far and I only have one plant that has sprouted plus the seeds are like a year old that's probley an other reason it's not sprouting.Planted like 10-15 seeds and only one has sprouted.It's pissing me off.So the veg. stage starts at 3-4 weeks,then when it shows hopeing it will show female do i automaticly change it to 12/12 to start the flowering stage,cuz I want my plant to grow as fast as possible to get the bud.

i normally change the fotoperiod to force my plants to show sex, but it is also partly due to hight restrictions, the only difference will b the amount of smoke u get

Well i think most of us have to change the light cycle to 12/12 to sex em.
I don,t know where you got your growing info but it,s all a bit mixed up, if you want to grow a nice plant then if i were you i,de get myself a basic grow guide for about £7 or so. It will save you £100s on your first harvest.
You will have an all you need to know step by step guide that you can pick up and flick throuh it when ever you want without having to ask on the boards all the time and wait for an answer.

Disco.........