clock off vs clock on

clock off

verb
  • Most of the staff have already clocked off for the night, you should do the same. 

  • to leave work, especially by recording the leaving time on a machine 

clock on

verb
  • To record one's time of arrival at work, traditionally by inserting one's card into a timestamping machine. 

  • To begin work at the start of the day or start of one's shift. 

How often have the words clock off and clock on occurred in a corpus of books? (source: Google Ngram Viewer )