you can veg after cloning for as long as you like. i've thrown rooted clones directly into the flower room and ended up with mini nuggets. they were cool as shit. or you can veg for a month and get a heavier yield. it doesnt matter in the end. what matters is what you want out of your grow. good luck
As Dannyboy wrote you can throw them into flowering right away when it's rooted, but 2-3 weeks in vegging first will probably pay off for the extra wait.