Good question, I don’t know if any studies have ever been done. In one way it makes sense, more light, more growth, more yield, but on the flip side, there are hormones that are activated to induce flowering by shorter photoperiods, so you might end up with semi-reveg looking buds???????
It's strain dependent from what I've heard. Some can flower at 10 hours of darkness some need 14. The 12&12 is the safest bet for flowering. I've even heard about cranking the girls back to 18&6 for the last 2 weeks before harvest trying to get just that little bit more. Does it work? Don't know I'm not the one testing it.