Service Time is the time you spend at each location. With this feature you have the ability to put pause durations at each waypoint so that the route calculation includes the time spent at each of the sites you visit. Fill this parameter to define how long you will stay at each location.
If all locations require the same service time, you should set it as default Service Time.
If each location requires a different service time, you should set it separately, next to each address.
The optimization process calculates all the possible routes and gives you the best route. Every route plan has the total route duration and the time it takes to get from one stop to the other. If you changed the service time to be bigger than zero, the time duration will include this as the time you should spend at each location.