There is a slight difference between gm and utc time, but not much. The difference is so small that I don't want to argue about it.

No need to argue when there's a source to cite.

Yes, and were it my preference the data would be in GMT/UTC until someone asked for it in another TZ. (And yes, I'm aware there is a slight difference in GMT v. UTC, but most people aren't aware of them until they hear about a "leap second", or the possible horror of a "negative leap second".) Unfortunately the data I am given includes time stamps from at least five different time zones, and it falls to me to compare them as part of other processing. Since Time::Piece is core and pops up periodically as a suggestion when questions arise about dates/times including TZs (such as a response to a post yesterday), I thought I should go ahead and post my question.

From https://www.apparent-wind.com/gmt-explained.html

Prior to 1925, astronomers reckoned mean solar time from noon so that when the mean sun was on the meridian, it was actually 00:00 GMT. This practice arose so that astronomers wouldn't have a change in date during a night's observing. Some in the astronomical community still use the pre-1925 definition of GMT in the analysis of old data although it is recommended that the term Greenwich Mean Astronomical Time now be used to refer to time reckoned from noon.

jszinger, thanks for the info!

In my work, I only process computer generated logging files and by definition of the "problem set", I never see any date/time before the "computer era".

But I enjoyed this info! Thanks!

I recommend using GM or UTC time for all values stored in a DB.
Use a a conversion module like Time::Piece for translation to
translate the DB time to a user time zone.

If my code is connecting to a database, I usually use that to do all the time arithmetic and conversion that I need...