I looked back at the 9.4 code for a few minutes, but much of the below is from memory as much as from reviewing the code today.

The monitors are updated whenever there is an update received from UeDelta.

The UeDelta service sends out a report to a specific MPS client when it detects a change in the data that has not been sent to that client. (I.e. there is a "delta" in the data, so that delta information is sent to the client.). If there are no changes within 30 seconds then a "noop" ("No Operation") update is sent, this will cause the MPS monitors to update their Last Updated Time, letting the end users no that the data on their screens is still current.

As far as I see, there is no local update directly caused by the MPS client receiving GPS. Of course if that data is being reported to Tracker, then Tracker will update the unit and that update will be a delta and will come back down to the client and update the monitor.