hard stop vs period of time

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 

period of time

noun
  • Synonym of time period 

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