Case When for date fields

Summary

Case when date is lesser than or equal to another date, THEN "on time", ELSE, "Not on time"

Content

I'm trying to build a Case statement that shows If one date is lesser than or equal to another, say "on time", else, say "not on time" (or some other decided upon phrase). Is that possible to do in OBIEE? Or can I only do Case statements when the the "Then" and the "Else" are other columns? Any thoughts on how to trick the column to do what I want it to do?