Time have to be in Race, not in a "gaming session".
Lazy way:I used Hotlap Modus - because there is no timeout - take a car and track that you want.
With controller use a rubber band that you drive slowly, and controller doesnt disconect. With wheel lay somethin on pedal or jam something in pedal that you drive slowly.
I think when you stand still you get back in menu or pit after some time.
Hard way:You also can do the Hard way and Drive 2 Hours a Race
100 Laps is max Value, for example 30 x 8min Laps on Nordschleife should take 2h