Let the whole pot dry out before you water. This pulls fresh oxygen into the soil and makes it available to the roots. If you keep the roots wet ... yeesh ... you are risking root rot. Pick up the pot with your hands - if it feels really light, then you need to water it.
Overwatering marijuana is a very common noobie mistake.
But you asked about vegging ....
I cannot afford to veg for too long becuse the growing season in Arizona is fairly short. Flowering needs to start in March because it gets so hot here by the end of May (I grow in an un-air conditioned boathouse). Once It gets to 95 degrees in the grow room - that's the end of the grow. So this means that I have to start flowering as soon as possible.
I agree with some internet advice I once read that for marijuana, the sprouting phase lasts until the first five fingered leave appears, then the plant grows towards maturity until there are three sets of fully formed five fingered leaves - this is the end of the vegetative phase, and time to begin flowering. Notice that for the three sets of five fingered leaves, each leaf stalk is symmetrical with the one on the opposite side. A "mature" plants, supposedly, will start growing non-symmetrical leaves.
Lastly, some people believe in vegging the plant as long as possible because they think it improves cannabinoid development, but ... I don't know about that.
I once had to to start flowering some Durban Poison three weeks after germination - the buds were small ofcourse, but it was still pretty stony weed.