another grow with question

hey every buddy i haven't been on the forums in a while haven't had a chance to do a grow due to living in apartments and rent houses. now i got my own house and have started a grow with 33 lil seedlings no exact genetics just green that i have gotten of the the past 3 years i would get a Q with one seed in it.

i have 400 watt hps and i was wondering when i can put the hps over the seedling and how far up from them? ill post some pics here in a few hours