User tasks (in general) often work with follow-up or due dates. Camunda BPM does support this by providing corresponding properties / members on the User Task BPMN. The Camunda API allows to filter user tasks by these dates so that due or overdue tasks can be found easily.
Beside the query filter also Timer Boundary Events on user tasks can be used to "detect" the maturity of a user task and to trigger an automatic action.
I implemented a working example to show the usage of timer boundary events on user tasks. You can find it at this GitHub location.