  Why Does the Space Shuttle Launch Countdown Have So Many Stops
and Starts?  In countdown-clock time, 43 hours really means 70
hours Kennedy Space Center countdown clock  NASA/Jim Grossmann
On July 5, if all goes according to plan, the final countdown of
the space shuttle program will begin. The launch clock at
Kennedy Space Center, a giant digital display with 40-watt
lightbulbs for pixels, will begin ticking down from 43 hours.
When it reaches zero, Atlantis will rumble off the launch pad,
and the final shuttle mission will begin.  But following a
shuttle launch is a bit like watching a football game—the time
on the game clock does not translate to actual time. And just as
a quarter in an NFL game takes much longer than 15 minutes to
play out, a lot more than 43 hours will elapse between countdown
and liftoff for Atlantis. In fact, roughly 70 hours separate the
planned start-up of the countdown clock, at 1:00 P.M. (Eastern
Daylight Time) on July 5, and the planned launch of the space
shuttle at 11:26 A.M.