Although it may be tempting to extend a pumping session to produce more milk, it is more important to focus on the number of times you pump instead of the duration of the pumping session. Since milk production is primarily dependent on demand, the number of pumping sessions plays a greater role in milk production and supply than the length of each pump. (The recommended amount of time for a pumping session is 10-15 minutes, however some moms may stop before 10 minutes if they have drained their breasts before then). This tip is especially helpful for mothers who pump at work or who choose to exclusively pump, since a key to maintaining milk production is making sure the breasts are drained enough times during a 24-hour period.
Sharen Medrano, Yummy Mummy Support Group IBCLC (www.nycbreastfeeding.com)