Only real people

But it's easier to say 6am or 6pm, only 3 characters than 4

It's better because it's impossible to confuse.

Besides, the "length" is the same all day long and shorter soemtimes too... it's always four chatecters.

When is dinner?
6:30 PM
1830 <-- better and fewer charecters.

When does the news end and the Tonight Show come on?
11:30 PM
2330 <-- again, shorter is better.

Ssshhhh imaginary people don't talk