<?php

$date1 = DateTime::createFromFormat("d/m/Y H:i:s", "06/05/15 08:34:32");

$date2 = DateTime::createFromFormat("d/m/Y H:i:s", "07/05/15 10:15:57");

$interval = $date1->diff($date2);

var_dump($interval->format("Le tout : %m mois, %d jours, %h heures, %i minutes, %s secondes"));

$totalHours = $interval->m * 730.4843 + $interval->d * 24 + $interval->h + 0.0166 * $interval->i + 0.0002 * $interval->s;

var_dump(sprintf("En heures : %s", $totalHours));