But I wish we could all just use one time. For some, midday would be 12, and for others it might be 19, but we already all use the same dates regardless of whether February is winter for one location or summer for another.
I'll take "better" even if better != perfect.
I think there is a simple plan that isn't disruptive. Simply require that all times be listed in both formats. For example, 9:00 am EDT (13:00 UTC) for all printed times on all signs, etc. moving forward from some day in the future. Eventually, we can drop the first as people adjust. (This is already how we re-number or rename highway exits)
This doesn't help in any way, shape or form. You have pissed off billions of people who have had to re-learn custom times for things, you have caused the weekday to flip in the middle of the day for billions of people, and you STILL haven't solved the problem of "Can I call Uncle Steve in Melbourne, or is he sleeping right now?"
There is no way to solve that problem of Uncle Steve (imo). But there is no difference in saying Steve is +8 hours so our noon is his 20:00 and or saying we should only call Steve between 03:00 and 20:00 UTC. It is an offset either way. It is only jarring to think that way now because it is the one way people have.
There is also the problem of someone driving across the US and suddenly they pass an invisible line and now it is one hour in the past or the future. The day changing while you work already happens for everyone working 3rd shift.
Billions of dollars in waste and confusion happen today because of forgetting about timezones. One study suggests that international trade is decreased by 5% per timezone between countries.
Also that system will probably devolve into defacto timezones without actual definitions where business in nearby areas decide on what constitutes reasonable hours based on businesses around them and the relative solar time but instead of reasonably crisp boundaries like you have today defined on a map it'll be a slow bleed and interspersing between multiple sets of '9-5' hours.
We are still trying to dig ourselves out of old systems where “today” and “yesterday” are logically different and we hide the problems by assuming most users are asleep at midnight. Most new systems don’t have this problem but older ones equate “tomorrow” with “start of business the day after tomorrow”.
There's probably some research somewhere estimating the cost to business (or loss of revenue) from mistakes in doing timezone conversions. In the simplest case, if you have a business call with someone halfway around the world, and one of you has recently gone into or out of daylight savings time, then there's a good chance the call will not happen when it should. Or perhaps you were supposed to be watching a political debate online at a given time so you could provide instant advice and feedback to advisors present in the debate, but you missed it because you didn't realize they had left DST a week before your location does.
I could go on and on with examples of the human cost to keeping the current system.
So let me say this: _coming up with the ideal system is not hard_. But how will you transition the world from its current state to this ideal state? Consider that the metric system (or SI), which is much better than the US system of measures, has still not been adopted in the US. Why? Because the problem of transitioning between systems is called politics.
But if you do much international travel, at some point you will encounter the problem where your various calendars, clocks, and other tools don't do the right thing (perhaps they get incorrect location information, or any number of other problems occur).
Then you have dis-information. If you don't realize it, then you will suffer by missing something important or wasting your time.
The tools are far from infallible now, and there's really no hope that they will ever work correctly.