title: How to calculate number of seconds between curent time and next Saturday using Java8
body: <p>I need to implement function </p>
  
  <pre><code>int secondsTillNextSaturday(LocalDateTime start);
  </code></pre>
  
  <p>Which does pretty same as it says, calculates number of seconds till next Saturday relatively to start time(if start is already Saturday, then it should return number of seconds till next Saturday after it). </p>
  
  <p>For example for 27.04.2017 00:00:00 (Thursday) it should return 2 * 24 * 60 * 60.</p>