I'm having trouble creating axioms that involve date properties (xsd:dateTime)

My ontology scope:

• It has a class Fall, where fall events with patients are individuals and it also has a data property dateCreated with range xsd:dateTime.
• There is another class Fall From Last Semester, which Fall individuals with dateCreated from the last 180 days are classified.

I tried with a fixed date (180 days before today) axiom:

It works, but I would like something like "dateCreated - today = 180", cause I won't have that fixed date in production.

Is there some way to do that with an axiom? Or I'll have to use some classes, separating day, month and year from the date?