yes they do ..but most of your growth is happening in the roots right now the more leaves they get the faster they can turn light into energy to grow hope this helps you a little
Id just stick with 18/6 or 20/4 because it simulates a somewhat natural light period. But im sure they do because buds develop a lot over night too. Ive also seen seeds sprout over night, so im pretty sure theres some vegetative growth.