In previous blogs, I addressed dating (which was my fiftieth blog – click here) and best practice principles on drafting numbers in contracts. This blog is about dates in contracting.
Best practice rule:
Prefer the 24-hour system to the 12-hour system. Include both the hours and the minutes (not the seconds).
When writing times, prefer using a colon over a point between hours and minutes. Do not add hrs or o’clock: 11:30 h. Use a.m. and p.m. (i.e., underscores separated by points) only when you apply the 12-hour system, to indicate the morning (ante meridiem) or the afternoon (post meridiem), respectively.
For midnight either write midnight or use 24:00 (for a period of time ending then) or 00:00 (for a period of time starting then). Despite the clear principle, in the case of midnight, a contract drafter should preferably refer to 23:59 h or 00:01 h, respectively, to preclude an (unjust but ‘intelligible’) claim that the contract was interpreted differently.
It is important to note that a reference to 12:00 p.m. is ambiguous. In view of the risk that a party relies on an erroneous combination of a.m. used in the 24-hour system, it is strongly recommended that a contract clause either refer to 11:59 a.m. or 00:01 p.m. as a marking point in time.
To indicate a duration use h:
…the time permitted for submitting bids is 12 h. after…
Distinguish summertime (the season) from summer time (daylight-saving time); for example Middle European Summer (MEST).
 For other denotations: <wwp.greenwichmeantime.com/info/timezone-summer.htm>.