moving photoperiod within flower cycle

I run a perpetual harvest so waiting for harvest to change the times of my light cycle isn't really an option.

Has anyone changed theirs during flower? Currently I have lights on from 8am to 8 pm but I want to change it up and have them on from 9pm to 9am.

Should I just change them by like an hour every three days? Does anyone have experience with this?

Any and all help is appreciated. Thanks

u can just do it all at once.. its better to leave em in the dark longer then in the light longer ya know