Provided are systems and methods for operating a mobile device of a first user that may include accessing a data repository to retrieve a first location of a future event scheduled at an event time to be attended by the first user and a second user, obtaining, from a position determination circuit of the mobile device, a second location of the mobile device, initiating transmission of a query to a route server to responsively obtain a time of arrival message including an arrival time for the first user to arrive at the first location from the second location, and, responsive to a difference in the arrival time and the event time exceeding a threshold duration, initiating transmission of a notification message that triggers a change in attendees that are physically present at the first location of the event without altering the event time of the event.