Drop to 18/6 save the planet, save your energy bill.
It's proven you gain no additional benefit from more than around 17.5/18 hours as the plant will naturally shut down. Some auto's can manage 20/4 but gain very little of nothing when compared to energy costs after 20/4.
The plant has to shut down as it need to switch it's chemical process from make food and sugars to transpiring and other natural processes. (This is why you get humidity spikes during veg with larger plants). Plants have a natural circadian (day and night) rhythms just like humans. These are governed by chemicals, hormones and plant genes. You take advantage of this chemical process when you switch the lights to flower.
The process of plant sleep is called Nyctinasty and you will notice after a while that your leaves begin to droop same time everyday (an hour or so before lights on) and perk back up about an hour after the lights have been on. This movement is called Nyctinastic movements.