They did a lot of tests ( in the Cervantes book) with autos and lighting. They tried 18/6, 20/4 and 24/0.
They reported that 20/4 was better than 18/6 and there was no difference in growth between 20/4 and 24/0.
It's cheaper to run 20/4 as your bulb should last 20% longer. Only advantage I can see to using 24/0 is that
you don't need a timer. Turn them suckers on and fugget about it. I personally believe some down time is good for plants
so I run autos at 20/4 exclusively.
Autos don't really veg. They go from seedling to flowering. If I remember correctly most autos jump from seedling to flowering
mode just about the time they show their 7th or 8th set of true leaves. Around 3 weeks in dirt.
Another thing about autos. Autos are fast growing. That means they live, reproduce and die faster than non-autos. So you
probably don't need the big pot they are in. I like to grow autos "hot". Small pots (fast), 1100W. lights (hot) and lots of nutes.
Most of the autos I grow hot are drying 60 days after getting in dirt. To do that you need small pots. I use 2 sizes for autos, 7-quart
and 3-quart. Small one is not as large as a gallon milk jug. Bigger pots = more time. works for me.
Good luck, BigSteve.