and midnight: use those words wherever possible to eliminate confusion. If numbers are required, noon is generally agreed to be 12:00 p.m. and midnight 12:00 a.m. (for 24-hour time, these would be 1200 and 2400). Within a printed or web document, be consistent by using only one format. In e-mail, it is OK to use the abbreviated format in the subject line, and then use the standard format in the body.