- var_dump: documentation ( source)
<?php
$dateAppointment = (new \DateTime());
$dtDuration = (new \DateTime())->setTime(1, 15, 0);
$duration = $dtDuration->format('\P\TH\Hi\Ms\S');
//var_dump($duration);
var_dump($dateAppointment);
$newDate = $dateAppointment->add(new \DateInterval($duration));
var_dump($newDate);