{entry_time} merge tag by Richard

// Title: create a merge tag of {entry_time}
// use a Hidden field and give it the value of {entry_time} you can then add the following code to your
// theme functions.php file to replace that merge tag with the time on submission.
add_filter( 'gform_save_field_value', 'replace_entry_time', 10, 4 );
function replace_entry_time( $value, $lead, $field, $form ) {
    $value = str_replace("{entry_time}", date("H:i:s"), $value);
    return $value;
}