I wouldn't do it.

One of the things I've noticed in reading A LOT of cannabis grow books is that they mainly all say to put the lights on a timer. I assume that means it would behoove one to get the plants on a strict light schedule and keep it that way, no wishy-washy'ness.

I've never heard other wise but I think swapping the lights back and forth is gonna throw off some sort of balance.

Even some expert growers will change their lights from 18/6 to 12/12 by changing the time only one half hour less daily. So basically they go 18/6, 17.5/6.5, 17/7, and so on until they reach 12/12 in the hopes of it being an easier transition for the plant. This too would lead one to believe that keeping the light sched strict is best too.

Or, do what I did. For the first few weeks I had my plants on 20/4. That cut down on the light bill just a bit but keeping you at 20 hours of growing goodness a day