DateTime is probably the slowest date/time handling modules on CPAN, but it also provides incredibly correct date/time handling. It can convert between timezones flawlessly; it handles those crazy leap-seconds we have from time to time; with the right plugins it can parse from and serialize into pretty much any format you need.

Apart from its speed, there are plenty of other things to dislike about it too: the objects are mutable which can allow for spooky action at a distance unless you remember to call clone all over the place, and it feels weird that from_epoch dies when called with a single parameter. But if you need correct date/time handling with support for timezones, it's the only game in town, so get with it! (That said, there is a DateTime subclass on CPAN called DateTime::Moonpig which cleans up some of DateTime's API warts.)

If all your times are in a single time zone, and you don't need to be pedantically accurate with your calculations (taking into account leap seconds, daylight savings, etc) then a lighter weight module like Time::Moment might be suitable.