Hey Growmie,
At this point, No, the plant is already in flower, so I wouldn't advise messing with the light cycle. The point of growing autos is that you don't have to change the light cycle for them to flower, so you're good at 20/4. Most people who grow autos use a 24/0, 20/4, or an 18/6 light cycle, I personally use an 18/6 light schedule. Feel free to shoot me a holler if you ever need any help, I'd be honored to assist you. Hopefully, this was helpful, and remember ... "Happy Growing" and "Free your mind one puff at a time".