Php -如何计算小时数？

$currentTimestamp = time();

$dateTime = date('Y-m-d H:i:s', $currentTimestamp);

$hours = date('H', strtotime($dateTime));

$startTimestamp = strtotime('2022-01-01 10:00:00');
$endTimestamp = strtotime('2022-01-01 15:30:00');

$startDateTime = date('Y-m-d H:i:s', $startTimestamp);
$endDateTime = date('Y-m-d H:i:s', $endTimestamp);

$startHours = date('H', strtotime($startDateTime));
$endHours = date('H', strtotime($endDateTime));

$totalHours = $endHours - $startHours;