To continue the above, here’s some additional information that may prove helpful:
I mentioned business keys in #2 above; you can get more information about them via the following link: https://blog.camunda.com/post/2018/10/business-key/.
Finally, here’s some information regarding the ability to set due dates on User Tasks: https://docs.camunda.org/manual/7.10/reference/bpmn20/tasks/user-task/#due-date. Note that it is possible to use REST API queries to retrieve a list of tasks that are overdue, and you could also specify additional filters, such as - for example - those required to only retrieve overdue tasks for a given process instance.
The time required to complete a process instance is highly variable based on the design of its process definition. When you consider the following information together, it’s possible to get a rough understanding of how much time might remain, however:
Where you currently are in the process instance. (See #2 in my first post above.)
The design of the process definition, i.e. those steps that remain.
Whether those remaining steps include wait steps, i.e. User Tasks or steps that wait for external interactions such as messages. If they don’t, then the instance will likely be completed pretty much as soon as the current step - possibly a User Task - is completed.