Why are my seedlings growing visibly?

We didnt understand the question i think, atleast i didn't. When you say " Started flowering from now on, and kept it on for 3 hours" do you mean you change the color of the light to a flowering light? Or the schedule? Also It would take more than 3 hours to switch your plants after switching the schedule. You can switch the light and keep the schedule, and even though the color is for flowering, your plants will stay in veg till you switch to 12h light/12h dark. Even after that, it will take a couple days for you to see the plant has flowering signs. I found that more mature plants take less time to switch visibly. Hope I helped ^^