Grow tent too hot

Presently the weather here is 100+ in the day and tent temp is at or just above 80 degrees. However, each night it cools down into the 60's. So even though I am in my 6th week of flowering-I would like to reverse the the 12/12 time period to 12 off in the day and 12 on at night. To do this I am either going to have to double up on a light or darkness cycle-then reset the hood timers. Which phase of 24 hour would be the least stressful to the plants? i.e. 24hrs of light or 24 hours of dark-before the new 12/12 cycle is started?

Thanks.

extended dark would be better but the best idea is to just decrease the daylight hours by an hour each day and youll be switched by 12 days from now.