title: Bash script for running two commands at specific intervals
body: <p>I was playing around with xbacklight program in linux terminal. </p>
  
  <p>What I am trying to do is, set my display to 0% brightness for 20 seconds at every 20 minutes. </p>
  
  <p>Briefly, something like: </p>
  
  <pre><code>in every 20 mins:
       xbacklight -set 0%
       continue this way for 20 seconds
  
       then:
           xbacklight -set 100%
  </code></pre>
  
  <p>How can I set these timeouts properly?</p>
  
  <p>Thanks in advance. </p>