Time::ParseDate at least is a date string parsing module (duh!), and it passes your items 1-3. Oh, and it was good enough for RT. :)

Whether you would consider it "robust" or "well documented" I cannot say. Item 5 is technically a pass, but if this ability is enough for your needs, I again wouldn't know. Still, as it is pure Perl, I suspect you'll find a way. :)

Might be worth looking into, if you haven't already.