24:00 versus 23:59:59--insights?

Adam Vartanian flooey at google.com
Tue Apr 28 15:23:26 UTC 2009

> There are a few places with rules such as "... lastFri 0:00 ..." that
> should be "... lastThu 24:00 ..."
> One possibility is to rewrite the rules that way; doing so buys error
> messages from pre-1998 versions of zic.
> Another possibility is to rewrite the rules as "... lastThu 23:59:59
> ..." which works with pre-1998 versions of zic but is a second off. A
> third way is to use 24:00 and, where it is used, include a comment about
> either upgrading zic or using the 23:59:59 dodge. I'd appreciate any
> insights on how to go forward.

I think it'd be better to have the rules state 24:00 if the transition
is at 24:00 (instead of either stating 23:59:59 or using the
23:59:59-means-24:00 solution).  I'd expect that users of an
11-year-old version of zic will be able to do the simple replacement
of 24:00 with 23:59:59 on their end, especially if there are comments
by the 24:00 values, and it's better to optimize for what I assume is
the much more common case of a user with a more recent version of zic.
 In particular, I feel like if either 23:59:59 solution is used it
will become standard practice, leading to either one second errors or
added interpretation complexity forever while providing benefit to a
small and continually shrinking set of pre-1998 users.

- Adam

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