time gained vs a photo? average photo plant needs 4-6 we4eks in veg then 8-14 weeks ( depending on the strain ) in flower. so your looking at 12 weeks minimum to grow plants that will produce good yield more likely 14-16 weeks. 10 weeks as an average for an auto although letting them go up ti 12 is not unheard of. so you'd still gain 2-6 weeks. If it was my setup, I'd start plants under each light, 2 weeks apart for a continual harvest. That also give you time to work on problems under one light if you have any. Also, I'd rather trim 1/2-2 pounds every 2 weeks than that whole tent all at once!!!
Also, have you considered your structural wiring? will you need a new circuit added to handle all the power needs of a grow that large? when you add up all the lights, fans, airconditioning, Dehumidifier, etc you made need an additional circuit.