When I first started working with Sesame I decided to do a date calculator for calendaring. I wound up having to stop because of a conceptual problem:
We all agree that "a week before" June 8 is June 1, etc.
What date is "one month after January 31"? "One month before March 30"?

I never
could figure out how to code "... uh ..."
The bottom line is that there is no agreement. You can't simply code an arbitrary decision. However
you define "one month" in those situations, various users will interpret "one month" differently--and then you'll wind up with inconsistencies, resulting in missed deadlines, parts ordered or products shipped early, etc.
Of course, there is also the risk that at some point in the future one of the bigwigs will insist, "That's
not what 'one month' is! From now on,
here's how we're gonna do it! ..." And then you wind up with search criteria scattered all over the place that have to be found and rewritten.