How do I create a workflow that will trigger the creation of a task X number of days after the last check-in?

What do I set for the task and what trigger do I use in the workflow? Checked in status = Not empty? with scheduled action for X days?

But then I suppose the problem becomes if they do check-in at some point before the task is created there will still be tasks created to remind them from the first check-in! Any way around this?