Expired Glympses remain visible for 48 hours before they are permanently deleted.
Expired Glympses are visible for a short period of time for two reasons. First, as a convenience for users who are trying to meet up. This saves the sender from having to send a new Glympse when a friend may just need an extra few minutes to navigate to their location.
Second, for users who like to post a Glympse of their location to their Facebook timeline. Since people tend to check Facebook periodically and sometimes just once or twice a day, this allows a sender to share their trail with friends and know that they won't just see a blank map because the Glympse expired earlier that day.