The package definition used by NIST (apparently RFC-867 doesn't define the packet very well) includes a flag which inidicates whether a leap second will be added or subtracted at the end of the month.

"L is a one-digit code that indicates whether a leap second will be added or subtracted at midnight on the last day of the current month. If the code is 0, no leap second will occur this month. If the code is 1, a positive leap second will be added at the end of the month. This means that the last minute of the month will contain 61 seconds instead of 60. If the code is 2, a second will be deleted on the last day of the month. Leap seconds occur at a rate of about one per year. They are used to correct for irregularity in the earth's rotation. The correction is made just before midnight UTC (not local time)."
 Since the leap second correction is always (with NIST) on the last day of the month, it would really only be necessary to check sometime before midnight on the last day of the month.

emc

" When in doubt, use brute force." — Ken Thompson

In reply to Re^5: Leap Second by swampyankee
in thread Leap Second by esskar

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