The light cycle functions within a range, so I don't think that one day of 45 minutes of difference will screw things up. For flowering, it's usually 12-14 hours on, and the balance off. Optimally, 12 on, 12 off. Just make sure that if you have those little lamp timers that you switch off the mode where it varies the time every day, so that a burgler can't figure out the houselamp is on a timer.