title: DispatchSourceTimer how to execute after repeating time
body: <p>I have a timer:</p>
  
  <pre><code>let queue = DispatchQueue(label: "com.domain.app.timer")
  timer = DispatchSource.makeTimerSource(queue: queue)
  timer.schedule(deadline: .now(), repeating: 30.0, leeway: .seconds(0))
  ...
  timer.resume()
  </code></pre>
  
  <p>It works perfect except one thing. Timer executes first iteration after my <strong>timer.resume()</strong>. But I need to execute first iteration <strong>after repeating time</strong> (in my case 30 seconds). How to do this?</p>