Each time the route distributor start the travel to a new destination, all pending arrival times are updated taking into account the total delay accumulated from the previous point. Only in this state is it certain that the service was delivered and the driver has already returned to the vehicle, thus completing the service time. Check how a route is completed from the driver application.
Each time the arrival times are recalculated, the client of the next destination is notified of the updated arrival time of the service. Customers after the next one are not notified because they can potentially have more delay as the route is completed.