This year I have been progressively adding B-vitamins (based on blood work) as well as taking them more consistently. It's a break out year for me in the gym, so I attribute some of that success (recovery) to the supplements.
However, B-vitamins make me hot and hyperhydrotic. Since I'm already a hot sleeper, I would hesitate to take them at night as I would expect them to disrupt my sleep more. Hence, I take them in the morning.