This is a small but surprisingly advanced example. It uses the Date plugin to get and format date information and compares the timestamps of the items to see if the due date is passed. I didn't add in time so you will have to figure that out but it is just the same as what is done. In the example, I store the date string. You could instead store the timestamp which would make it harder to find and edit manually but again, I'll leave that up to you to work out.
Good luck with your project.