I don’t know if this helpful, but maybe you make two properties. One would be the time left as active, which is what you have today, and the other would be days expired. It wouldn’t be the same property but this workaround might help you get where you need to be. From there, you might be able to create a third property and use a workflow to populate it based on the values of the other two. That’s if you need it all to be in one property. I haven’t tested this with your use case but I do something similar with properties we use to get things where I need them for reporting.