No, I implemented only the subset of the Date API I needed for the application. A fully-fledged Ruby Date would be a larger project.
+1 for duck typing, a custom non-Date object can look like a date for operations that only use a subset of the methods.
How many other people have half-started implementations of the same thing? That's why it's important to publish your code somewhere, even if it's "not good enough". Someone else can make it good enough.