You could veg them to fill your space, or you could naturally let them grow and flower almost as autos, if it's 12/12 from start. I always veg them for at least a month to form them and make them strong before putting out flowers, and after switching it usually takes 10-12 weeks of flowering. So you may count average term for photo, it's 15-20 weeks from seed. Clones are separate story
I will try to make good instruction how to form photos, please see my grow diary time from time, i will put some good info there.