Time for a nooner.
NIST, 12:00 p.m. is the instant immediately after the clock changes from 11:59:59 to 12:00:00.
"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."