php excel 讀取日期問題

PHP讀取日期2020-03-07 讀入到php中后變成了43897

需要處理成正常的時間戳！

$data['start_time'] = PHPExcel_Shared_Date::ExcelToPHP($data['start_time']);
$data['end_time'] = PHPExcel_Shared_Date::ExcelToPHP($data['end_time']);