No, you can change from 24 hour to 18 without a risk of flowering. When you go from 18 to 12 that will start the process. Also have read quite a few times on this site that if you put plants into 36 hours of darkness between veg and flower it resets the plants internal clock to accept flower faster.
tinytoon Reviewed by tinytoon on . First timer Hey everyone just starting up and need some advice if someone can help. If i start with 24 hrs of florescent light and then switch to HID on a 18 hour cycle when ready will that cause the plant to flower? Thanks for the help. Rating: 5