its best to keep it set where its at, but if you have to switch, gradual is the key. just replicate mother nature's slowly shifting seasons. 15 minute intervals per every two days oughtta be okay. i myself encountered the same situation and thats what i did. no problems whatsoever.

the only waste of time as far as gradual switching goes is to gradually switch them to 12/12 from veg. it doesn't do anything beneficial, imho.

stay safe
-GG84