Given a DateTime object that is set to the first second of the year 2017,...

$datetime->format(‘%Y-%m-%d %h:%i:%s’)

$datetime->format(‘%Y-%m-%d %h:%i:%s’, array(‘year’, ‘month’, ‘day’, ‘hour’, ‘minute’, ‘second’))

$datetime->format(‘Y-m-d H:i:s’)

$date = date(“Y-m-d H:i:s’, $datetime);