Alternatively, consider killing the boom brothers a bunch of times because they sometimes drop legendary/orange rarity items that are extremely powerful. Which would end up saving you some time as you proceed.
In addition, redoing some parts of missions doesn’t hurt because you get XP and get stronger in game, better gear, and you get more skill points and you learn the game. All that adds up to you being able to do that area faster. Eventually you’ll be strong enough and good enough to run that entire area in 10 minutes or less. And you’ll feel badass because of it.
I’d say that going forward you will be able to get to good stopping points within 30 minutes everywhere in the game. That’s how I played BL2 and video games for a while too. I loved Borderlands 1 and 2 because I could open it for 5 to 60 minutes and always make progress. Compared to games like Destiny or mostly standard shooters, I often found myself feeling like I wasted time.