Photo-Period grower. I haven't grown any autos yet at all.
I regularly veg under 16 hrs light. Why? To save on electric costs. I wouldn't try this with an autoflower plant though as it's on a time clock and slowed growth means reduced yield. Anyway, at the end of the run at harvest time, I doubt you'd be able to tell that I cut some daylight out for affordability. I'm pulling 4-6 oz per plant per run. So yes, with a photo plant you can do that. Do you want to? That depends because those lost 2 hrs of light daily usually show up somewhere (can lengthen veg time a bit for example) ... but if this change to 16 hrs means everything is running during off-peak hrs, you will likely still be ahead on your electric bill. For a more precise answer, you'll have to do the math.
Now with that said, I am running Tropicanna Poison Fast version photo period plant. It's a fast flower plant. It will flower at 16 hrs of light. These are going in my greenhouse but I'm starting them inside with 20 hrs a day until they get transplanted outside in late June.
