A good rule of thumb to use with plants you have no experience with is to switch when they are 1/3 of the height you want them to finish at. This will give you enough room to finish flowering a great majority of plant types. Under a 400w, that means switching at about 8" tall. Not all plants will triple in height during flowering, however, and some grow even more than that. Different types of training can decrease vertical ghrowth during flowering and allow the plants to be vegged taller before switching.
i guess it depends on how much bud you're trying to get, but I would veg for at least another 2 weeks so they get some size and have a bigger yield.