PANIC!
Patriots. Are. Now. In. Control.
T-27 hours and holding
This is the first built-in hold and typically lasts four hours.
Clear launch pad of all non-essential personnel
https://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html
T-11 hours and counting
Activate the orbiter's fuel cells
Clear the blast danger area of all nonessential personnel
Switch the orbiter's purge air to gaseous nitrogen
(clearing all non)