Well, if you just search for “date” at http://search.cpan.org, you will today get 5000 hits ...

Some suggestions of packages that I have used very often:

• DateTime will do absolutely anything with a date.   Takes a bit of time to grok its examples, but once you do, it’s worth it.
• Date::Manip is another object-oriented interface for dates.   Again, there is a learning curve.
• Date::Simple ... well, it’s simple.   Put down your Swiss Army® knife and grab this pocket-knife which happens to have the blades you use most often.

But there are literally thousands more, including some pure-fun ones.   Search as-above for “DateTime Calendar” and then get your time-machine ready:   DateTime::Calendar::Mayan, DateTime::Calendar::FrenchRevolutionary, DateTime::Fiction::JRRTolkien::Shire ...

The one thing you don’t have to do in Perl is to “write your own” routines to handle positively anything that has to do with dates/times.   I find it very convenient to use the packages which define a date-time object, i.e. “this thing ‘is a’ date/time, its internal implementation is blissfully opaque, and I can tell it to do things and ask it questions and It Just Works.™”   Functional interfaces are much more baroque due to the sheer number of options that must be supported by a thorough handling of dates.