title: how to override Extjs Timefield to show custom max value
body: <p>I want to display 11:59 as the maxValue for ExtJs timefield with increment=30. I set maxValue as "23:59" but it did not work, and shows 23:30 as the maximum value. Can anyone specify which function/code to override to display 11:59 as the maximum value?</p>
  
  <p>Thanks in advance. </p>