People log in to Facebook on both mobile devices and desktop computers, both at work and at home. How it's used depends heavily on the audience.
According to Quick Sprout, the best time to post on Facebook is 3:00 p.m. on Wednesday. Other optimal times include 12:00–1:00 p.m. on Saturdays and Sundays and 1:00–4:00 p.m. on Thursdays and Fridays.
Engagement rates are 18% higher on Thursdays and Fridays, and weekdays from 1:00–4:00 p.m. tend to see the highest click-through rates. On Fridays, Facebook use spikes by 10%.