Manipulating/changing the photo period during veging or flowering

Hello and good day all
right now i am flowering some plants and i have my lights set to come on at 7am and off at 7pm. i am wanting to switch it to on at 7pm off at 7am....will this hurt my plants? I am 1 and 1/2 weeks into flowering and i would hate for them to revert back to the vegetaitve stage. Any help with this would be greatly apprectiated!

let it go off at 7pm then wait 24 hours (keep the fans running) and turn it on at the next 7pm for 12 on, 12 off.