This should work:
$ddtcounter1="2014-03-06 20:15:30";
$ddtcounter2="2014-03-07 21:20:30";
$date1 = new DateTime($ddtcounter1);
$date2 = new DateTime($ddtcounter2);
$diff = $date1->diff($date2);
$hours = $diff->d * 24;
$hours += $diff->h;
echo $hours;
echo $diff->i; // Minutes
echo sprintf('%s.%s', $hours, $diff->i); // Hours.Minutes