well you have a choice of eighter 24 or 18/6 your plants will grow fine with eighter.
myself i prefer 18/6 if your electric bill is a consern you will want to go with 18/6.
IMO, seedlings getting 24 hour light tend to be tighter noded and bushier.
I do 24/0 until 12/12, but it's fine to start under 24, then after the plants are established, change over to 18-6 or whatever.