Web traffic from mobile devices sees a sharp drop off overnight, and then gradually grows over waking hours in the US, finally peaking at the end of the day, eastern standard time, generally around 8 pm to 10pm.
The data suggests that users start to use their smart phones and tablets at about 5 am, with traffic building through the day until about 10 p.m.
PC web usage is much more constant across the day. Mobile Web Traffic Up 35% in Under a Year