hard stop vs uncertain period

hard stop

noun
  • A definite time when someone must end a task in order to meet another time commitment. 

  • A mechanical device that limits the travel of a mechanism. 

  • A tactic used by armed police to stop a vehicle believed to contain dangerous criminals. 

  • Synonym of full stop 

uncertain period

noun
  • An unspecified amount of time 

How often have the words hard stop and uncertain period occurred in a corpus of books? (source: Google Ngram Viewer )