This has to be 10 hours (real time) on a single save game. It is cumulative, it does not have to be in a single session, and is known to sometimes unlock a little late.
If you set farm sim to run at 1x time, you can walk away for hours if you really want to grind this one out. If you are just achievement hunting, chances are with the contact system, you are going to be pretty close to 10hours anyway.