I pump for 35mins...
Usually my breasts have stopped milking after about 28mins....but I keep going in hopes for the alleged "2nd letdown". But no such luck yet..
When does your 2nd let-down happen? What power level do you pump on?
ETA: I have the Medela Freestyle (it's a double-eletric for anyone who doesn't know) and it is pretty good at emptying the breast.