reschedule photo period

I currently run -- noon to midnight, but after observing the temps I think it would be better to go from 6pm to 6am.

How do I make this change? Or can I just "do it" and they'll be fine?

One plant is ~3weeks into flowering, other is just now showing pistils. ( in case that matters)

transition so that they have one long light period - extra light can't hurt them - some people do 24/7 light - it would be the irregular dark period that could confuse them..