It could stay the 24h/day time format, but timezones are a pain - I always have to recalculate them for local time. Why couldn't everybody work with UTC?
And by the way: when will we finally get rid of the daylight savings time?!?
Now suppose we all had the same time. If I phoned them just before lunch, which would mean shortly before 12:00 in the UK then I'd have to try and figure out what Japan would be doing at that time. Would 12:00 in Japan be early morning, late at night, would they be eating a meal, would they be at work? Now I have to remember where in the day different times are for different counties. However, with timezones all I need to remember is a numerical value and I can easily figure out where Japan is in the progression of a day (i.e morning, evening, night).
So that would need the same exact effort.
The man benefit would be for the "let's meet at the same time online" etc coordination stuff -- where's its brain-dead easy when everybody has the same time.
I guess calling would also be easier if the used system can show if the other side is available like Skype or even better when she is available.
A) Everyone uses UTC. Now you have to know the business hours in Tokyo because it is not universally 8-6 anymore.
B) Everyone uses local time. Now you have to know their local time.
I don't know where you are, you don't know where I am. I tell you I am available from @300-@800 if you want to Skype today. Let me know which time is good for you.
Or you have to try to figure out the whole no work on Friday thing in the middle east and Monday being part of the weekend. You always have to look it up.
What made this dream cool in the digital age is I could just have hours that I'm available and if I wanted to work late at night, I could. I considered myself a 'hardcore hacker' in '98 and what appealed was how well this lined up with my natural inclination to hack on code from 10pm to 5am every day, despite being in high school.
I didn't care or need to know where my IRC friends were. We could collaborate none the less.
But it's really meaningful only in the sense that it's early morning, so that the same information could be conveyed by saying "I had to catch an early-morning flight." (More precise information than that could always be conveyed: "I had to catch a flight 1 hour before sunrise", or whatever.)