var schedstart = Xrm.Page.getAttribute("scheduledstart");
var interval = 15;
var timeField;
var tables;
var table;
var row;
var cell;
var time;

if (schedstart != null)
{
   timeField = schedstart.all.time;

   //Check the existence of the time field. It is null if the control is setup to only display the date.
   if (timeField != null)
   {
      //The new interval in minutes.
      tables = timeField.getElementsByTagName("table");

      if ((tables != null) && (tables.length > 0))
      {
         table = tables[1];

         //Remove all existing values from the selection box
         while (table.firstChild != null)
         {
            table.removeChild(table.firstChild);
         }

         //Add the new values
         for (hour = 0; hour < 24; hour++)
         {
            for (min = 0; min < 60; min += interval)
            {
               row = table.insertRow();
               cell = row.insertCell();
               time = ((hour < 10) ? "0" : "") + hour + ":" + ((min < 10) ? "0" : "") + min;
               cell.setAttribute("val", time);
               cell.innerText = time;
            }
         }
      }
   }
}

setTimeInterval: function (ctrl, interval)
{
   var control = Xrm.Page.getControl(ctrl);
   var timeField = control._control._element.children[0].children[1].all.time.children[1].firstChild;
   var row;
   var cell;
   var time;

   if (timeField != null)
   {
      while (timeField.firstChild != null)
         timeField.removeChild(timeField.firstChild);

      for (hour = 0; hour < 24; hour++)
      {
         for (min = 0; min < 60; min += interval)
         {
            row = timeField.insertRow();
            cell = row.insertCell();
            time = ((hour < 10) ? "0" : "") + hour + ":" + ((min < 10) ? "0" : "") + min;
            cell.setAttribute("val", time);
            cell.innerText = time;
         }
      }
   }
}