I don't remember how long it took me, really it takes as long as it takes to fill up what your boob will fill up... does that make sense? Like sometimes one boob would be really full and so it would fill up the bag in 8-10 minutes, but other times i'd do 15-20 to get it full it I was having to do a lot of compression, etc.
Are you working FT? You will most likely need to pump more than twice. I worked 9 hour days and I'd feed the baby at 6, pump at 9, 12, and maybe 2:30 or 3 (something like that) then we'd have a nice breastfeed nap at 4-5 when I got home. I can't remember the exact schedule but I know I pumped 3x a day when I worked that long. I did that for 5 months. When I moved and my house was closer, I pumped again at 9, went home and fed baby at lunch, then usually pumped again in the afternoon unless I got off early (if I left at 2:30 or 3 then I wouldn't pump again- just go home and feed baby), I did that for just over 4 months. I was able to BF until he was 13 months but only pumped until he was barely 10 months old.