If just go to search.cpan.org, select "Modules" in the drop-down menu and put "Date::" in the search window, you'll get lots of solutions to choose from.

For a bare-bones, core-modules-only way to convert dates from strings to unix "seconds-since-the-epoch" numbers, look up "perldoc -f localtime" for conversion of unix time to calendar numerics or string, and "perldoc Time::Local", whose "timelocal" function can convert calendar numerics to unix time.

For more elaborate modules that do more for you and might make your job easier, consider Date::Calc or Date::Manip.