>Most of the world uses a 24 clock, so you get it only once. Most people in the US use am/pm, so we get it twice.
>
>>Once. Unless you share the common illusion that the day has 12 hours twice. We learn that it has 24 hours.

I tend to use 24-hour notation over the "conventional" 12-hour notation to avoid ambiguity -- something that most "normal" people find odd (especially when someone says "we'll meet at 6" -- I have to ask "do you mean 6PM or 6AM?"). I usually have to remind them that it's not unusual for "computer people" to keep strange hours.