People who want to maximize their Gold earning will start an activity, then set a timer and attempt to complete the activity just after the 12-minute mark. Gold payouts used to vary by activity, but Rockstar has streamlined the payout system so that all of these activities pay consistent Gold amounts.
So the longer you take to do any Gold-earning activity, the more you’ll be paid. In any activity that pays out Gold, you are rewarded for how long you play.