Time zone flipped

[Arthri]

Hello! I noticed a weird issue on the Meta Discourse forum, the GMT +/- time zones seem to be flipped. GMT +* is interpreted as GMT -*, and vice versa.

Take this timestamp:
2022-02-13T07:00:00Z

It displays like so on my side:

Taipei’s time zone is GMT+8, therefore 15:00 or 3:00 pm is correct.

However, when observing explicit time zones such as GMT-12 and GMT+12, their behavior seems to be flipped. GMT-12 is displaying the time appropriate for GMT+12, and GMT+12 is displaying the time appropriate for GMT-12. I’ve mentioned earlier that Taipei’s time zone is GMT+8, I’ve also explicitly specified that at the bottom, and it’s observable that the date shown is completely different from Taipei.

As a reference: these are what the correct dates should look like

[sam (Sam Saffron)]

Wow odd bug, thanks for reporting it, we will have a look.

[david (David Taylor)]

Conflict between timezones in "Insert date / time"

I’m afraid the technical reason here is pretty confusing - you can read about it at Moment Timezone | Docs POSIX compatibility requires that the offsets are inverted. Therefore, Etc/GMT-X will have an offset of +X and Etc/GMT+X will have an offset of -X . This is a result of IANA’s Time Zone Database and not an arbitrary choice by Moment.js. Thus, using locality based identifiers is preferred over fixed-offset identifiers. So, in IANA’s Time Zone database, Europe/Oslo is currently equivalent…

[Arthri]

Ah, that explains it, this post also helped me understand what was going on

Time zones `Etc/GMT`, why it is other way round?