Due date in User task is not working

I used the user task in flowable. My requirement is, that user tasks should wait for a maximum of 15 minutes. It should close once it has reached the max time. If I trigger the event within 15 minutes, then the user task will proceed with the respective flow and end. Once the user task reached the due time, it should end automatically irrespective of the message event.
My problem is:
I tried to stop the user task at a particular time. So I used the due date in the user task. I tried all the mentioned " Due date" date Time format in flowable documentation to stop user Task. But I’m unable to achieve it.


according to documentation here dueDate is just a metadata field, so you would have to send/create the event outside of model (not shown in your screenshot) that would then interrupt the user task. no automatic action will happen because dueDate has been achieved or passed.