Dont use 24/0 max 20/4 in veg even better is 18/6. If they are autos use 20/4 all the way. And you can start flowering if you want it all depends on the size of the grow space. Plants can double in size in flowering stage. Some people leave their plants 4 weeks others 6 weeks in veg. It's a personal preference. When you dont allow enough veg time plants tend to have a more immature (less tasty)and less potent end product.