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

Dave Cantor Dave at Cantor.mv.com
Tue Apr 28 16:12:44 UTC 2009

On 28-Apr-2009, Olson, Arthur David (NIH/NCI) wrote:

> 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.

Strictly my personal opinion, I think that we should use 

A related question:  is it possible for a jurisdiction to specify 
a rule that says something like the time change will occur at one 
minute after 24:00 on the second Thursday?   That's not the same 
thing as 0:01 on the second Friday.   It's 0:01 on Friday after 
the second Thursday, and there is no current way to express that 
(that I could find).  Do we need to allow times like 24:01 or 
even 25:00?   I don't need answers now; I'm just raising the 
questions for thought.   Perhaps we shouldn't worry about it 
until and unless something like that happens.  I think it's 
unlikely, but possible, for awful rules like that to occur.

Dave C.
Groton, CT

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