title: How to use 24 hour clock when invoking showTimePicker() in Flutter?
body: <p>when I'm invoking method showTimePicker() in Fluter it shows me a picker with 12-hour clock (uses AM and PM periods). Also when I invoke format() method on TimeOfDay object it returns value in 12 hours system.</p>
  
  <p>How do I change it to 24 hours clock? I've found that I need to change alwaysUse24HourFormat property in Window class but i have no idea how to do it.</p>
  
  <p>Could anyone help me?
  Thank you in advance for your answers.</p>
  
  <p>edit:
  code is shown below:</p>
  
  <pre><code>    Future&lt;Null&gt; _selectTime(BuildContext context) async {
      final TimeOfDay response = await showTimePicker(
        context: context,
        initialTime: pickedTime,
      );
      if (response != null &amp;&amp; response != pickedTime) {
        setState(() {
          pickedTime = response;
        });
      }
    } 
  </code></pre>
  
  <p>edit2:
  i tried this only with Android.</p>