Hi. I’m retired and have consuming cannabis since I was 14 years old. Just started growing in a 3x3 tent and have 4 pretty girls that are quite healthy using Peter’s 20x20x20. So, I’m in the newbie category. My four young girls are getting 12hrs of light. Would it hurt them if I change the lighting to 18 hrs or should I leave them at 12 hrs to be safe?