En-route stop time period

When planning a route with en route stops, how long does Waze allow for a stop? Can I adjust the period of an en route stop?

For example I need to be at point B at 11:00 but need to stop at point A en route. I expect to be at point A for 20 minutes, what time do I leave home to be at point B at 11:00 allowing for the stop?

Waze will alert time to go, no matter if you are at home or not, if you enable GPS localization to always.

In your example, you can save for later both destinations or just point B and Waze will always alert at time, even your are driving late for your first destination.