Joseph I'll go you one better, and say that my seedlings all fold their seed leaves up together at night (peppers especially and more than tomatoes), and they do so at 'bed time' whether the lights are turned off or not!
Many's the evening I looked in on the seedlings and found them all hands up, say sorry guys, and turn the light off for them.
The leaves are flat open in the morning before I get up.
Night length is more important than day length, I believe all these peps and toms need a solid 8 hours of darkness. Maybe 'leafs together' is a way of going dark?