When are the best times to pump?

When you can. It depends on why you are pumping. If you are engorged, pump until your breast is compressible before the start of the feeding. If you exclusively pump, try to pump 8-12 times a day. If you are pumping or build your supply or store milk for future use, after nursing is a good time. You don't ever have to pump- since the best "pump" is the baby, but if you have a reason to, pump whenever you can.
After nursing. Assuming your nursing your infant as well, the best time to pump is immediately after your infant finishes nursing. This way you fully empty your breasts, which also signals your body to increase it's milk supply.