There is a much easier solution to get the 10 hour achievement. Load up any mission past the prologue. One you beat the mission the clock will stop. You can then idle for as long as you want. I would go to bed and wake up. Walk out the door and all the time you spent idle will count. The only risk is your game crashing over night. It does not matter if you controller turns off during the night. You will only get credit for all the hours you spent idle if you successfully walk out the door.
This solution can also be used to boost the hours played on each class to unlock skills that require you to play long hours on a certain character.