Php: DateTime: how to set only seconds (not hours neither minutes)

Is setTime elegant?

$my_date->setTime ( $my_date->format("H"), $my_date->format("i"), $new_second_val );
$my_date->setTime ( $my_date->format("H"), $new_minute_val, $new_second_val );
// etc...

Just set the seconds to "00"

date_default_timezone_set('America/Sao_paulo');
$date = new DateTime();
echo $date->format('Y-m-d H:i:00');