title: Calculating time difference in 24-hour
body: <p>I need to subtract two 24-hour time values from 0 to 23.</p>
  
  <p>For example, 21:00 - 22:00 should return 23 hours and not -1 (!) hours.</p>
  
  <p>I don't care about minutes.</p>
  
  <p>I tried searching but couldn't get one. But I feel there's already a function for it, so didn't bother to write one.</p>
  
  <p>Thank you, all.</p>