There's no time like the present, unless it's 12 a.m. or 12 p.m., when some experts say there's no time at all.
Those two hours are the trickiest times on the clock. No one, not even Uncle Sam, seems certain whether 12 a.m. means midday or midnight -- or if 12 p.m. is lunchtime or bedtime.
At the Government Printing Office, the nation's publisher, 12 p.m. is acknowledged to mean noon, at least most of the time.
Railroads avoid the issue by using schedule times like 12:01 a.m. or 11:59 p.m. Blinking bank clocks generally let passers-by figure out for themselves what "12:00" means.
And according to the nation's official timekeeper, the Naval Observatory here, there is no 12 a.m. or 12 p.m., only "noon" and "midnight."
"Technically, there is no such thing as 12 a.m. or 12 p.m.," Joanne Petrie, a Transportation Department lawyer who oversees matters of time zones and standard time, said in a recent interview.
Faced with the timeless question earlier this year, judges in New Jersey threw out a $15 parking ticket given a man who parked at a meter posted with the hours "8 a.m. to 12 p.m."
Arriving at the Wildwood, N.J., meter at 1:30 p.m., the driver assumed he could park free any time after noon.
But he was fined by a judge who ruled that, while the meter read "12 p.m.," town officials actually wanted paid parking from morning until midnight.
The state's second-highest court disagreed, saying bewildered motorists had to be given the benefit of the doubt from the wording on the meter.
"It is inherently ambiguous," said Dr. Gernot Winkler, director of the Naval Observatory's Time Service Division.
But even the observatory, which relies on sophisticated chronometers to keep exact time, can't seem to straighten out the matter to everyone's satisfaction. "We have calls all the time," Winkler said.
He explained that the abbreviations "a.m." and "p.m." by definition are not suited to differentiate midday from midnight. They refer to "ante meridiem" and "post meridiem," or the times before and after the sun passes directly overhead.
As such, Winkler explained, neither can be used to exactly describe the middle of the day itself. "The noon moment is an exact moment in time," he said.
The confusion mirrors the overall misunderstanding about whether midnight ends or begins the day.
Scientists, to understand each other, usually agree that the day begins at midnight. But Winkler noted that the Internal Revenue Service gives taxpayers until the end of April 15, or midnight, to get their tax returns postmarked.
At the Transportation Department, Petrie said she's concerned about standard and daylight time -- a jurisdiction the department inherited from the early days of confusing, cross-country railroad schedules.
But as a government official with jurisdiction in time matters, Petrie said she also gets plenty of calls on the 12 a.m.-12 p.m. debate.
Many questions come from lawyers, trying to sort out legal time references. Other inquiries come from doctors, trying to figure out what time to put on a birth certificate.
The Naval Observatory has prepared a pamphlet on the issue, with the advice to the time-conscious not to use either 12 a.m. or 12 p.m. The observatory recommends using noon or midnight.