What strain bro? Indica or sativa dominant?. Full on equatorial sativas can take 3-5 weeks to even show 1 hair.
My Malawi took just over 3 weeks to show 1 tiny hair. Try switching it to 11:30/13:30(on/off) to push the plant into flowering faster, I put pure sativas on 11/13 to stop them from growing out of control and a faster harvest, but indicas will most definitely suffer from this light cycle.
What's your setup? make sure to leave everything on the plant at this stage mate.
Good luck and welcome to Roll It Up