I ran the OPs code on a linux system and didn't see an error about timezone. Maybe the OP didn't have such an error either.
Older versions of Date::Manip need to be told the time zone when running on Windows, but were generally able to determine the time zone from the system on *nix platforms. Documentation for current version of Date::Manip suggests it tries to get the time zone by reading the registry on Windows, so it may no longer need to be told - I haven't tried current version on Windows.
I am guessing you are running an older version of Date::Manip (5.x) on Windows and the OP is running current version on Windows or any verson on some other platform.