title: detect 15 minutes elapsed time from datetime.now
body: <p>I have a timepicker and I wonder how I can make it detect if the selected time in the timepicker is 15 minutes ahead of the <code>DateTime.Now</code>.</p>
  
  <p>If I set the timepicker to 9:15 and the <code>DateTime.Now</code> is 9:31 I should get a message that I only can set the time 15 minutes ahead the actual time.</p>