24/0 to 12/12?

Im running 24/0 light schedule. I was going to switch to 18/6 after seedling stage but I kinda got lazy and didnt do it. Now my plants are like 15 inches tall. Could I switch my light schedule to 12/12 from 24/0 or should I do a few days with like 20/4 then few days 18/6 before I make the full transition to 12/12? I dont want to stress them out cause I know if plants get stressed they could go hermie? any advice would be greatly appreciated. thank you.

Straight drop to 12/12 from 24/0 has always worked for me no hermies as a result. If you graduate the light hours down like you wanted I don't see any harm either.

Some people do a 48 hour dark period to help triggger flowering faster.

Going straight to 12/12 won't stress them. If anything, 24 hours of light would do more stress than that. You should be fine, but you will want to throw the switch soon, they are getting a little tall.