title: Convert UTC ISO string date to Unix timestamp
body: <p>I have this UTC date in a Google spreadsheet: <code>2018-10-18T08:55:13Z</code> and would like to convert it to Unix timestamp (<code>1539852913</code>). I tried this formula, but it's unable to recognize the timevalue:</p>
  
  <pre><code>=DATEVALUE(MID(A1;1;10)) + TIMEVALUE(MID(A1;12;8))
  </code></pre>
  
  <p>If I can get a valid date and time, I can use this formula to convert to Unix timestamp:</p>
  
  <pre><code>=(A1-$C$1)*86400
  </code></pre>
  
  <p>Does anyone have a solution for this?</p>