Yes you can use that, and I am as it's the best I have, but it's an overall number.
So, for example, if you had 200 days left on memory and 300 days left on CPU that number would show 200 but if I had an alert for each one being less than 1 year I would have wanted the system to fire two alerts one for memory showing 2000 days left and one for CPU showing 300 days left.