$updateQuery = "UPDATE application SET OT_Rate='".$_POST['OT_Rate']."', Time_Start='".$_POST['StartTime']."00', Time_End='".$_POST['EndTime']."00', Reason='".$_POST['reason']."' WHERE Emp_ID='".$_GET['empID']."' AND Date_OT='".$_GET['OTDateYear']."-".$_GET['OTDateMonth']."-".$_Get['OTDateDay']."' AND Time_Start='".$_GET['OTStartTime']."00'";
mysql_query($updateQuery);
You missed an single-quote ( ' ) after this:
SET OT_Rate='".$_POST['OT_Rate']."',