A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Time
Numbers
Part III. Style 20 spelling

For references to times of day in even increments of an hour, half hour, or quarter hour, spell out the times, with a hyphen between parts. If necessary, specify in the morning or in the evening. You may use o'clock, although it is now rare in research writing.

The participants planned to meet every Thursday around ten-thirty in the morning.

When emphasizing exact times, use numerals and, if necessary, a.m. or p.m. (lowercase, roman, no intervening space; see also 24.4.1). Always include zeros after the colon for even hours.

Although scheduled to end at 11:00 a.m., the council meeting ran until 1:37 p.m.

In either situation, use the words noon and midnight (rather than numerals) to express these specific times of day.

For use of words or numerals in dates, see 23.3.