inverting times of light/dark periods while switching from 18/6 to 12/12

I was wondering how much can a plant be affected, if it's on an 18/6 cycle and let's say that light go out now between 6pm, and 12am. You want to switch the to 12/12 cycle but have the lights out at different time, let's say 5am to 5pm lights out. Will this change in bio rythm or bio-clock stress to much and cause plants to hermie? Would giving a 24+hour dark period before the switch help against that stress?

Thanks in advance for sharing you experience and thoughts on the subject.