I've been trying for years (by example) to popularize using PT, MT, CT, ET. Since it's always after a number ("Are you avail at 4ET?") there has never been one instance of confusion, and I save typing and avoid the small but real possibility of being interpreted too literally (suppose someone asks a computer "What time is 4:00 PM EST in London time" during the summer, and gets a 'technically correct' answer).

I don't have a similar answer for GMT/BST though.

This is the kind of imprecision that enrages me, though, because I am a resident of Arizona, and we observe MST all year long. It is currently MST. It is not MDT here. Therefore if we say, like, "it's 4:33pm MT" here and someone presumes that we are in DST, they would be wrong, and they would make the wrong conversion.

That is exactly why I am enraged by "EST"-users out of season. Because they are deliberately insensitive to people who are actually in Standard Time.

But it actually seems to be deeply ingrained into American-centric corporate culture. I had a WFH job in a large company that was nearly 100% WFH, and they consistently used "EST" to their detriment. And I kept challenging this apparently-unwritten policy, and they just said "it's always been this way". And this month I've even caught UPS using it: yeah, the United Parcel Service was quoting transit times for one of my parcels in terms of EST, which was utterly nonsensical to me.

It seems that people don't mean "Standard Time" anymore when they write "EST" but simply "EaStern Time" and it is implicitly understood by human communicators to definitely not mean Standard Time except when it does. I went around with Gemini LLM about this for awhile. I cannot explain why people would embrace an obviously incorrect acronym, but they really have.