Most efficient way to update ETAs of stops based on vehicle progress during the day?

Love the GraphHopper planning features that let us plan our routes during the day. My challenge is using GraphHopper efficiently to update the ETAs for the incomplete stops on the route while the route is in progress.

As the route progresses during the day, based on the vehicle current lat/long and incomplete stops, we want to be able to update and monitor the dynamic ETAs on the incomplete stops and compare them to the time windows established for those stops. If an ETA for a future stop is drifting later than the requested time window, the goal is to alert the dispatcher. Is there a way to do this efficiently without pinging the optimization API without the vehicle?

Ideas welcome. Wonder if the Matrix API can be utilized in an ongoing way.