you will get many different opinions on this but i would say to go 18 hours on 6 hours off from germination to the point you would like to flower.
20/4 work too and even 24/0 but i would always let my plants have that rest because at no time does mother nature leave her lights on 24 hours and i for damn sure would be pissed if someone took my sleep time away
Then switch to 12/12 on/off obv haha. This induces flower, just make sure you leave room for the plant to stretch after you induce flower.
This is a very basic question as far as growing goes so PLEASE read these forums and learn up before you go much further.