Heat problems!! HELP Please

I am currently running 18/6 5am-5pm my temps today we’re getting to 90 degrees in my tent. I was thinking about switching to 9pm-9am when temps are cooler. So question is will it hurt my plants if I switch the timing being they are use to 5am-5pm

5am-5pm is 12/12. Are you saying you are about to switch to 12/12? If so it shouldnt be a problem to change from 9pm-9am when you do.