Q. For a poster, is the following correct, “Friday June 17th 8:00 pm,” or does there need to be a comma between Friday and June?

A. If the words are all set on the same line in the same type size and color, then yes, you need a comma after Friday. Chicago style does not put th after the day: “June 17” says it perfectly. You also need a comma after the date, and Chicago style uses periods in p.m.:

Friday, June 17, 8:00 p.m.

The same information could appear on a poster without any punctuation, however, if the position, type size, color, or other design elements clearly separate day, date, and time.