title: excel date/time format specification not converting text date/time to internal date format?
body: <p>I'm getting time stamps as text from a log and need to get excel to ingest this so it recognises it internally as a date/time format so that I can do math with it. It comes into the excel sheet as a copy paste operation.</p>
  
  <p>The timestamps are in format: 2013-07-11 20:00 so I've formatted the cells where this goes as: yyyy-mm-dd hh:mm. </p>
  
  <p>For some reason however I still can't do math with those cells, e.g. subtracting one of those date/times from another results in #VALUE.</p>
  
  <p>This in Office 2011 on Mac.</p>
  
  <p>Any clues anyone?</p>