Why do so many cultures accept using colons to separate divisions of time (posted around 08:30:45 local time) but none of them use it for separation of general numbers? (It is sometimes used for division or ratios, i.e. 10:1 for 10 to 1 odds.) Seems like we could use units (like with measurements) or prefix units (like with currency) to indicate different uses for numbers, and maybe ratios just use double colons?

Designing programming languages, you will spend way too much time obsessing over things like this. Some languages use underscores as a grouping separator. What about bases? Exponential notation?