php excel 读取日期问题

PHP读取日期2020-03-07 读入到php中后变成了43897

需要处理成正常的时间戳！

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