Why is Time Important?#

A lot need to have accurate time and the our usage of ntp was for eDirectory. In eDirectory time is one of the components used to determine the order of changes that take place within the eDirectory full multi-mastered environment. In the eDirectory environment, it was important that time be the same amongst all servers, not that it necessarily be the right time.

As we have moved into doing a lot of SAML and other federation work, the requirement for time to be the right time is now critical as the certificates used in most federation agreements are very short lived. (like in the 2-3 minute range)

When is Midnight?[1]#

When someone refers to "midnight tonight" or "midnight last night" the reference of time is obvious. However, if a date/time is referred to as "at midnight on Friday, October 20th" the intention could be either midnight the beginning of the day or midnight at the end of the day.

To avoid ambiguity, specification of an event as occurring on a particular day at 11:59 p.m. or 12:01 a.m. is a good idea, especially legal documents such as contracts and insurance policies. Another option would be to use 24-hour clock, using the designation of 0000 to refer to midnight at the beginning of a given day (or date) and 2400 to designate the end of a given day (or date).

When is noon and midnight?#

This is a tricky question because 12 a.m. and 12 p.m. are ambiguous and should not be used.

To illustrate this, consider that "a.m." and "p.m." are abbreviations for "ante meridiem" and "post meridiem," which mean "before noon" and "after noon," respectively. Since noon is neither before noon nor after noon, a designation of either a.m. or p.m. is incorrect. Also, midnight is both twelve hours before noon and twelve hours after noon.

It is fair to say, however, that the shortest measurable duration after noon should be designated as p.m. For example, it would be applicable for a digital clock changing from 11:59:59 a.m. to 12:00:00 to indicate p.m. as soon as it the 12:00 appears, and not delay the display of the p.m. by a minute, or even a second. The same is true for midnight, but there is an added issue of which day midnight refers to (see below).

Hours of operation for a business or other references to a block of time should also follow this designation rule. For example, a business might be open on Saturdays from 8 a.m. to noon or weekends from 3:30 p.m. until midnight.

Time And Epochs#

And you often need to know about Time And Epochs.

More Information#

There might be more information for this subject on one of the following:
[#1] http://www.nist.gov/pml/div688/times.cfm

Add new attachment

Only authorized users are allowed to upload new attachments.
« This page (revision-7) was last changed on 07-Jun-2014 08:38 by jim