It's best to pump as often as your baby would nurse and about the same times, if that isn't feasible, try to pump as close to that as you can. And honestly that will probably be most comfortable for you anyway, being engorged and leaking is not fun. And I'd pump 15-20 minutes unless you are able to get a ton out in less time than that. You can probably cut yourself some slack since it is only a 3 day trip, but from my pumping experience working FT, my body adjusts very quickly to a lack of demand, so I wouldn't want to slack off too much. YMMV though!