$date = '2021-12-31'; $time = '23:59:59'; $db_daydatetime = strtotime("$date $time"); echo $db_daydatetime; // Output: 20211231235959
$db_daydatetime = 20211231235959; $date = date('Y-m-d H:i:s', strtotime($db_daydatetime)); echo $date; // Output: 2021-12-31 23:59:59Based on the examples provided, it is likely that the package/library being used is the standard PHP datetime library, which provides functions for working with date and time values in various formats.