A lot of great information has been shared here. When I went back to work at 12 weeks, she was feeding about every 2-3 hours.
When I started I fed her one side in the morning and then on my way to work I pumped the other side. This really helped!
Then at work, I pumped three times in a 9 hour day (8 hours work, 1 hour break time for lunch/pump).
When I got home I obviously didn't pump but nursed at 5:30 when we got home and then again at 7:30 before she went to bed. Usually she was up only once a night.