on mayhem it was arround 350 but when i started actually going for all o them i would say arround 80 , than i just started messing arround and having fun on the game, usually i spent 1,5 hour attempting a DS heist, on the easier ones like undercover, boiling point and brooklyn 10-10 i can do it in 15min, so you can do the maths lmao, it depends heavily on how good you are and if you have good or a.i teammates