You can use strtotime
:
$start = strtotime("07:00:00.0000000");
$end = strtotime("16:30:00.0000000");
$difference = $end - $start;
Or with DataTime object :
$start = new DateTime("07:00:00.0000000");
$end = new DateTime("16:30:00.0000000");
$interval = $start->diff($end);
$difference = $end->getTimestamp() - $start->getTimestamp();
Then echo
the result :
echo $difference; // in seconds
echo $difference / 60; // in minutes
echo $difference / 3600; // in hours
echo $interval->format('%s') // in seconds
It's then up to your preference. I also suggest you to have a look at this post regarding the performances of the two solutions.