shortest veggong time???

im starting some new babies unfortunatly i dont have 2 rooms only 1 for flowering, however i have managed to put together a rubbermaid which i plan on using for vegging my question is what the shortest time possible to veg for without any downfalls? take in mind i have a decent space for flowering.
thanks any replies get thanked with some rep

btw using cfl for vegging and a 400 w hps for flowering, space is 4x2x6 and the rubbermaid is 2x1x2

you can flower right from seed if you want....i usually try to veg at least a month or two, the bigger the plants when they go into flower the more bud

forget cfl just buy an mh bulb if that ballast is switchable...but 2x1x2 is def not enough space just use the same space as the first veg room flowering room