title: Ensure User has entered string in correct format?
body: <p>Whats the best way to ensure the user has entered a valid time string such as:</p>
  
  <p>5:24
  5.4</p>
  
  <p>102:30
  102.5</p>
  
  <p>It will be entered into a UITextField therefore will be in a NSString.</p>
  
  <p>I want to allow the user to enter the time in either hours and minutes (hh:mm) or hours and decimal minutes (hh.m).</p>
  
  <p>In the hours minutes example they should be able to enter as many hours as the like but only between 0 - 59 minutes. With the hours decimal minutes I want them to only be able to enter again as many hours as the like but decimal minutes can only be 0 - 9.</p>
  
  <p>Many Thanks</p>