pumping at work advice?

I've been fortunate enough to take six months off and my daughter has been EBF during this time. I'm going back to work in a week and want some advice about pumping! how often in an 8 hour period do you pump? do you always pump for set amount of time like 15 min? has your supply kept up after a few months? my LO sometimes snacks every two hours at home but she can go up to four hours between feedings. thanks!!