How I knew this: 
https://groups.google.com/forum/#!topic/bit.listserv.ibm-main/ylLbkY32dM4 

Can't seem to find OA14062 anymore.

I am not so negative on z/OS time support as you are but all of these little 
buglets kind of amaze me. I appreciate that this is tricky stuff to get right, 
with all of the boundary conditions and so forth, but if I were writing 
STIMER-type support for a million-dollar operating system I would try my 
damnedest to get it perfect.

Charles

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf 
Of Paul Gilmartin
Sent: Friday, July 03, 2015 2:07 PM
To: [email protected]
Subject: Re: Leap Second today!

On Fri, 3 Jul 2015 13:13:32 -0700, Charles Mills wrote:

>> the syntax of STIMER macro provides no way to specify a time past 
>> midnight
>
>Au contraire (assuming "STIMER" includes STIMERM). I issue
>
>         STIMERM SET,LT=MIDNITE,EXIT=POP_MIDNITE,ID=ID_MIDNITE,        +
>               ERRET=ERR_MIDNITE,PARM=AWORKAR,MF=(E,STIMERML_SET)
>
>all the time, where
>
>MIDNITE  DC    CL8'00000100'       Midnight + 1 second 00:00:01.00
> 
I hadn't known that, nor was I able to suss it out from the Manual.  May I 
assume that if you issue your command at 00:00:00.5, the timer pops in another 
0.5 seconds, which may or may not be what you intend.

Ugly.  If STIMER LT is issued close enough to the requested time it's 
unpredictable, depending on code path and dispatchability, whether it waits for 
0.01 second or 863399.99 seconds.

Ugly; ugly!  If the request is for an interval, just add it to the TOD value 
and load the Clock Comparator.

If the request is for LT or GMT, compare to current time,  If the requested 
time is less than the current time, add a day.

If GMT, adjust for leap seconds when they occur.

If LT, adjust for leap seconds and Daylight Saving Time boundaries when they 
occur.

My head hurts.

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