title: When does `int * time.Second` work and when does it not in golang?
body: <p>Why does <code>time.Sleep(5 * time.Second)</code> work fine, but:</p>
  
  <pre><code>x := 180
  time.Sleep(15 / x * 60 * time.Second)
  </code></pre>
  
  <p>does not? I get a type mismatch error (types <code>int64</code> and <code>time.Duration</code>). Given the error, I understand more of why the latter fails than why the former succeeds.</p>