This is why servers and military use UTC.

Yes. GMT is UTC (meaning GMT is +0 and synchronized with UTC), therefore if you have to work out what time it is in other time zones, you use UTC. Your application shows the time in your time zone (unless otherwise specified). Responses will also be shown in your time zone.

Yes, when you are comparing times across time zones, you can use UTC time. (UTC is essentially a more modern GMT, there are differences but only the nerds care.)

You will want to use all times in UTC. But be aware that when you do this, any times that are meant to be the same throughout the year will shift one hour due to Summer Time/DST. Not every region does summer time, and the ones that do start and stop at slightly different times. (And Southern Hemisphere countries do it in Northern Hemisphere's winter.)

If that's too inconvenient for you, or most of your users are in your country, an alternative is to explicitly state the chat hours in your local time zone, with the understanding that it will shift a hour vs. UTC twice a year, and anyone outside your country's summer time rules will just have to deal with it.

Swatch internet time

https://youtu.be/hovFbHt3L3w

EDIT : Is... this racist flash cartoon actually on the actual official swatch yt channel?

https://www.youtube.com/watch?v=4ROTh6gZz3Y

https://www.youtube.com/@swatch/videos

As a web developer we almost always store times in UTC, we simply convert it to the user’s time zone while displaying it. I prefer to use the browser’s time zone when doing this, but it could also be a saved user preference or even determined by figuring out the geographical location of your IP address (not a fan).

There is Swatch Internet Time (.beat), which was invented to:

… simplify the way people in different time zones communicate about time, mostly by eliminating time zones altogether. It also does away with the division of the day into 12 or 24 parts (hours), then 60 parts (minutes), then 60 parts (seconds), then 1000 parts (milliseconds). Furthermore, there is no confusion between the AM/PM system and 24-hour time.

For example:

Internet time clock

There is, just use Hammertime. It's used on e.g. Discord to automatically convert Unix time* into the respective time for everyone.

* A time measure that is in 'ticks' from 1970 and on.

Even if multiple people are online at the same time: why is time inconsistent (the sun is up in one place while it’s dark in another), you can ask friends what time it is in where they live (internationally) but receive different responses based on their surroundings. This person states it’s 08:00 while you reply it’s 23:00 on the same day with one difference: they’re starting the day while you’re about to finish it moving to another.

This is the price of living on a oblate spheroid.

As others have said, using UTC is the most reliable solution to communicating times across time zones. Everyone only needs to know their own offset (which might change twice a year if their location uses DST). A handy way to mark times as UTC is to attach a “Z” as in 20:00Z, which is part of the international standard covering dates and times ISO 8601.

There is.

On the Internet it's always 2am.

That would be meaningless for translating to anything else, such as the time zone where any participants are.

Which is why everything uses UTC/GMT and offsets for local time

Because the earth doesn't stop turning and somebody will always be asleep.

We used this a lot at work:

https://www.timeanddate.com/worldclock/meeting.html

Put in your timezone and the other people’s timezones and you can see what hours work for everyone.

Also, GMT isn’t the same as UTC. GMT is only the same as UTC for half the year, then it changes to BST (British Summer Time).

https://www.timeanddate.com/time/gmt-utc-time.html

There's lots, but just like everything, very few people actually can stick with and use them. Probably the thing that I think would be a logical feature in most chat programs, would be if say you put in your timezone into the client somewhere, then when you type a time you put some character before it like *3:30pm - the chat client could determine your timezone, put it in chat as UTC, and each recieving client could automatically convert it to their users timezone (and I suppose some kind of tag to make it so people know it is already translated to their timezone).