You're really gonna be pushing it to get anything worth smoking in 8 weeks, but if you gotta i'd say veg for 2 weeks and flower for 6. I'd try reducing light for flowering from the recommended 12 to 11 at the third week of flowering then 10 and 9 each week after, this way the plant will react to the shortening of day and should finish a little earlier. I'd go get some lowryder seeds if i was in your position, start to finish 10 weeks, you should get a decent smoke after 8 weeks but i'm afraid any other seeds it's just not gonna be long enough. Hope i'm wrong. Good luck dude
Oh and get a fan as soon as you can, and look into getting a heat shield or cool tube as well. HPS lights are a nighmare for heat!