When is this a problem?
This is most often seen in a transactional list when creating a unique value for an item to import to a list.
Why is this a problem?
Thinking about this from a list creation point of view, do you really want to create a new list item for every date, or do you want to create the list item once? If you include Time as part of the key, your list will be unnecessarily large.
How to correct:
Dates are data and should not be part of a code. Remove the dates and use time references outside of the list.
Check out the Transactional section of Data Hub Best Practices
Questions on this topic? See Does the list use Time as part of the key? in our Model Optimization Checklist forum.