Wow, lot's of discussion spawned by your questions,
@BubbaKush909. Nice. I'll take my shot.
Seems you're asking about two things basically, when to harvest and how much light per day to give them.
On When to Harvest: For me, I will almost always, auto or photo, defer to my trichomes and go basically by them, harvesting when I have the amount of amber I want. My suggestion, on autos or photos, is to forget about what any of the seed sellers say about harvest times, other than having it in the back of your mind as a rough (VERY rough) estimate. The style of growing, latitude you're at, environment, amount of light, quality of light, nutes, etc....there are a million factors that determine when a plant is ready. In my experience, RARELY does a plant finish when the seller says it will. If I'm growing outside, I may go a bit less by trichomes just cuz in my very limited outdoor experience I found trichomes were less accurate an indicator than they were under LED in a tent grow. But trichomes will always be my first indicator. After that I go by the "look" and "feel" of the buds. Are there white hairs popping everywhere? Not ready. Are the red hairs all sticking up and not yet curled into the bud? Not ready. Are they still dense-ing up? Not ready. Etc.
So I use kind of a combination of those two, trichomes and observation. Example: right now the Strawberry Lemonade is done. All her trichomes are almost all white. I could take her tomorrow and likely pluck her right near the peak THC production, which is all white, no amber. But that's a bit too "coke-weed" for me, I like to go 10-20% amber. This plant is less than 1% amber. But she "looks" ready. It's an indoor tent grow under LED, I am deferring to her trichomes. If I went by observation alone I'd have harvested her and taken her way too early.
The other thing about autos in particular I've noticed is that they often will get a second wind right when you think they are getting done. Like, the next day you go out and suddenly they're covered with white pistils AGAIN. That seems to happen frequently if you don't take them too early. Autos and this "they're done so much faster" thing is largely bullshit truth be told. If you veg a photo for a month then flip it it takes the same amount of time as an auto.
And no, autos do not flower faster, they flower in normal time frames in my experience. The speed is all in veg.
On Light Amount: First, lemme clear this up for sure:
YOU DO NOT CHANGE YOUR LIGHT HOURS ON AUTOS TO INDUCE FLOWERING. This is the single biggest difference between autos and photos. If you ae going down to 12/12 on autos to promote harvesting, no wonder you're having issues.
As far as how much per day, I've tried 18/6 with autos, 24/0, and 20/4. My opinion: 18/6 is too much rest, you are depriving them of light hours when they can be productive. 24/0 also doesn't work (generally, does with some strains and I suppose for some people, but I would argue they'd do better otherwise). Maybe you can go 24/0 until you start to see pistils and preflowers, but from that point forward the plant needs rest daily. SOME amount. For me I've found that 20/4 works best, and I run them that way start to finish every time.
That's my experience. Hope that's helpful.