You should veg until they look rdy for the flip Imo. I don't ever really count veg days, I measure height because I have height constraints out the waazhoo. But you can think the same way. You have a tent correct? Probably 5 or 6ft tall minus the pots height and the ballast at the tippy top minus the space the plants need in-between the light, probably leaves you with like 4ft-3.5ft of actual grow space. If plants double in size when flipped to 12-12, you can get em like a ft n a half tall before switching to bloom. If you do it that way you have more time to top them n get em bushier, build a scrogg, n the longer in veg the greater the end yield will be. Basically I'm just trying to say don't think about veg as a set time you have to follow, think of it as the time you have to get the plants rdy for bloom. Just get em healthy bushy n as many tops that'll make colas to the top of the plants before they out grow the space you have.