The first MN reward
The average time it takes to receive the first reward is calculated in hours with the formula millions_locked_before_your_MN_is_enabled*2.6/60. At the time of writing the total number of millions that are locked in MNs is 3,500 million, so 3500*2.6/60=151.67 hours or approximately 6 days, 7 hours and 40 minutes.