Light cycle is really dependant on your needs and your space. 24/0, imho, is not a sane scheme. It robs the plant of her nightcycle, in which it develops roots and rests. Imo, this is just as important as having enough light.
18/6 is a normal lightcycle, you would use this when you have plenty of vertical room, and want the most from your plants. Plenty of light is needed here too, as taller plants means your lights will hang higher = further from lower buds.
I use GLR. GLR is 12 hours of light, 5,5 hours dark, 1 hour light, 5,5 hours dark. This limits the plants growth a little, making her more bushy, which is nice in smaller growspaces. The one hour of light in the middle of it's night cycle, will trick the plant into staying in veg. It takes about 4 days after switching to flowering, for them to show it.
I mainly use it for cost saving on the utility bill, but it works pretty well, and I see no real reason to start wasting more energy .. as I seriously would not know how my vegging plants can be improved, except more sane LST and pruning.
If you have auto's, mind you that they will determine for themselves when they will flower, regardless of your light schedule. You can place em under 24/0 and have them go to flower.
You avoid issues in this case, by making sure you flip to 12/12 (or 11/13) at 3,5 week veg for your auto. Either that, or veg the WW outside your tent when your Auto goes to bloom. All you need for decent veg, is 3 23w household CFL's @ 6500K colour temp. Forget all other nonsense like fans and stuff in that case .. they are not needed that much that they will f-up your plant
