do it right now. If you are only 7 days into flower cycle switch to 24/7 of light for the next week or two. Don't worry it will flower again when the others catch up. The problem is the light will be very high for the new plants when it's perfect for the others. Is there a way you can raise the other plants until they catch up. You donā??t want them the same height but close so they get enough light.