Do lots at home. If you can feed your baby as you drop off at daycare and as you pick up-that's 2 "pumping" sessions done. Plus, you get to know your day care provider a little better and don't have a crying little one as you go home. Use your free (non-work) time to get the baby to breast, because the baby is the best pump. Weekends are great for that.
Pumping at work. If you want to maintain your milk supply, you will need to pump about every 4 hours. If your baby is over 4 months and breast feeding is well established, you may be able to pump less. Slowly increase the amount of time between pumping, and pump just enough to relieve engorgement, but not enough to empty the breast. Over time, your body should produce less milk during work hours.