I may be wrong here, so umm, don't shoot me, but I believe that epoch timestamps are always given for UTC. Time::ParseDate does some manipulation depending on what your timezone, but there's a whole lot of options to tell T::PD how to handle the input time, so you could tell it that all dates being given to it are from a certain timezone (ie. before the date that you changed the timezone, tell T:PD to use one timezone, afterwords, tell it to use another) and that should pretty much straighten out any inconsistencies you have.

I might be wrong about the epoch thing, but you can most certainly make up for shifts like that in T:PD itself.