I myself found auto's to grow fast, and I did mine on 12/12 because I had a photo plant in with them. This was my first auto run at day 79 from sprout. Will do another run of them this summer outside so they will be done before thieves are out looking for plants.
I actually studied this a couple years ago, by looking at the photo and auto versions of the same named strains from the same breeder. The autos had about 10% less thc. For example, if NorthernLights photo is 15% thc, then NorthernLights auto was about 0.9*15% ~ 13.5%. As more and more good breeders tackle autos, their quality is rising.
My northern lights original was 20 percent THC auto and my gelato was 26 percent thc auto. I got friends who have smoked for 40+ years and get stoned from the auto's I grew. Autos today are nothing like they were when they first started them.
Those thc numbers are just what the breeder puts on them. both auto and photo breeders alike lie about that. Im saying comparing the autos ive grown to the photos ive grown, the photos were ~20% stronger than the autos on average. Ive gotten seeds that claimed 25% and were likely much closer to 10%.
Back in the 90s some of the best skunk bud that got you stoned was only 12 percent thc. Today weed is alot stronger now because of the genetic crossing and money to be made on seeds.