PHPExcel Date Format

Though it is unclear what are asking, If you are looking for a date conversion

 // convert old date string to YYYYmmdd format
    $date = date('d M Y', strtotime($old_date));

this will output date in 09 Aug 2012 format

Is your problem in getting the date from MS SQL as a date/time, or setting the Excel date?

There is a whole section of the PHPExcel documentation that explains the use of the PHPExcel_Shared_Date::PHPToExcel($PHPDate) and PHPExcel_Shared_Date::FormattedPHPToExcel($year, $month, $day, $hours=0, $minutes=0, $seconds=0) helper methods for converting PHP dates to an Excel datetime stamp value that you set as the cell value, and then you apply a number format mask of one of the date masks such as PHPExcel_Style_NumberFormat::FORMAT_DATE_YYYYMMDD2 to that cell

Instead of

$t_year     = substr($xls_column_datas["colname"],0,4);    
$t_month    = substr($xls_column_datas["colname"],5,2);    
$t_day      = substr($xls_column_datas["colname"],8,2);
$t_format   = '=date('.$t_format.')';
$objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow($data_column_num, $data_row_num, $t_format );
$objPHPExcel->getActiveSheet()->getStyleByColumnAndRow($data_column_num, $data_row_num)->getNumberFormat()->setFormatCode('[$-C09]d mmm yyyy;@');

try setting

$t_year   = substr($xls_column_datas["colname"],0,4);
$t_month  = substr($xls_column_datas["colname"],4,2);  // Fixed problems with offsets
$t_day    = substr($xls_column_datas["colname"],6,2);
$t_date   = PHPExcel_Shared_Date::FormattedPHPToExcel($t_year, $t_month, $t_day);
$objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow(
    $data_column_num, $data_row_num, $t_date 
);
$objPHPExcel->getActiveSheet()
    ->getStyleByColumnAndRow($data_column_num, $data_row_num)
    ->getNumberFormat()->setFormatCode(
        PHPExcel_Style_NumberFormat::FORMAT_DATE_XLSX14
    );

$date = PHPExcel_Style_NumberFormat::toFormattedString($data, "M/D/YYYY");