wpdatatables_filter_formdata_before_save exists in the wdt_ajax_actions.php file but is not described in the documentation. While is really helpful when you need to add auto timestamp for example.

If someone need such function can grab some code:

function timestamp_for_wpdatatables ( $formdata, $tableId ) {   

    $columnsData = WDTConfigController::loadColumnsFromDB($tableId);
     foreach ($columnsData as $column) {
         if ($column->orig_header == "timestamp") {
                 $formdata["timestamp"] = date("Y-m-d H:i:s");
         }elseif ($column->orig_header == "created" && get_query_var('new_created_for_wpdatatables') == true) {
                $formdata["created"] = date("Y-m-d H:i:s");
         }

     }    
    return $formdata;
}
add_filter('wpdatatables_filter_formdata_before_save', 'timestamp_for_wpdatatables',10,2);

function created_for_wpdatatables ( $formdata, $tableId ) {

    if ($formdata['wdt_ID'] == '') {
        set_query_var('new_created_for_wpdatatables', true);
    }
    return $formdata;
}
add_filter('wpdatatables_filter_frontend_formdata', 'created_for_wpdatatables',10,2);

This can auto-increment datetime into columns with headers "timestamp" or "created"