You can veg two months and flower in a 5 gallon but a 7 would be better. Once you have nice preflowers flowering time isn't going to get shorter than that you will just yield more with a longer veg. A half pound a plant is reasonable with one plant and two months veg so you will have plenty. Training and the strain you grow are going to factor into yield too. I would top early and lst it into a scrog to maximize your yield.i vegged two plants for two months and they take up my entire closet from end to end.