How does it differ from 'mixed punctuation' and closed punctuation'?

open punctuation is omitted closed punctuation is a colon

Mixed Punctuation means simply applying a colon at the end of any salutation.

Open Punctuation Open, closed, and standard punctuation are all methods of punctuating a business letter. Although any of the styles can be used, closed is seldom used here in the USIn an Open...

i believe there is a comma. but i also believe there can be a colon. Ex: There are many kinds of fruits such as, bananas, oranges and apples. Ex: There are many kinds of fruits such as: bananas,...

If by "am" you are referring to time, below is an example of Associated Press style: 10:30 a.m.