With an experienced, semi-skilled team, both available missions can be beaten in around 30 minutes. I am sure if a team focused on running a mission as quickly as possible there might be times in the low 20s, but the best I have done with random teams is just over 30 minutes without playing with any real sense of urgency. We just did not mess around and everyone performed well.
If it is taking your team longer than an hour, something is going wrong. It may just be that your team is new and does not understand the mechanics of the game or the mission objectives, but I do not think the missions themselves are to blame. You could have just drawn some weak teammates (it happens, sometimes my runs take 45 minutes or so due to some, ahem, “baggage” that needs to be carried).
I think targeting 30-60 minute missions is just fine, though. Gearbox cannot really be accountable if a team takes three hours because that is far, far outside the norm. I do feel for you, though. I am not a leaver, by any means, but I do think if my team was doing that poorly I would bow out for the sake of my sanity, so good on you for powering through.