Got all quests in 2 hours (because i got the Merit Hoarder thanks to the Clock Watcher one). Mainly because of lag and a LONG time trying to get the highest rank. Btw, the Rank 4 gun is a 1 hit 1 kill weapon but it's only one ammo and takes a while to reload. Aside from most puzzles, don't bother with it. Just buy it for the medal and try to get Rank 10 so you can get the GAU-17 and basically break the game because it makes the game extremely easy.
If u play it for quests only, it is easy and can be done in 1 hour probably. But if u are trying to buy and fully upgrade all weapons it will take more time.
It doesn't really take that long. You can farm money very fast if you just do the first 4 Elite Jobs again. With the Perk from lvl8 they give ~950 gold each and take less than 5seconds. That might not be the most fun way to farm money, but i think it's the fastest. The only thing that takes longer than 1hour to get is the "lay for 2hours" merit
I got all the quests, including Bob. The quests lag quite a lot in here so you gotta wait quite a few moments after completing it before it notices. Best if you don't do anything except exiting the mission when you get the afterbriefind. That's how i got it.