Will increasing my light hours in veg make my plant grow faster?

Just wondering. Was watching a vid on youtube, and this guys plants had grown a relatively more than mine in 3 weeks because he was doing a 21 light, 3 dark hour cycles. Im doing 18 light 6 dark right now.

i do 24/7 and they seem to love it

There is countless controversy over this and I think as with most environmental conditions it ultimately comes down to the genetics. Some plants thrive in sunlight while some are perform better in a more shaded environment and too much light can be a bad thing. You will have to try out different cycles on your strain(s) to get the answer to your questions. The 2 common light cycles are the ones you mentioned, 18/6 and 24. There is also 12-1, which is 12 hours on, 5.5 hours off, 1 hour on, and 5.5 hours off. The idea behind that is the plant only needs 13 hours of light to maintain a veg cycle. Truth is, they all work, however...there is definitely an optimum amount of light your specific strain will want per day. It's up to you to maximize the plant's growth through trial and error (unless it's a known strain with past experimentation completed). Basically, anything above 13 hours of light per day will keep your plants in vegetative mode. Pick a # and run with it and see how your stuff performs.

ive read here before that the plant needs the dark to grow...it stops photosynthesis as soon as the dark cycle starts. but id say "Dubdeuce" advice is pretty spot on