Calculating date difference more precisely in PHP

function datediff($interval, $datefrom, $dateto, $using_timestamps = false)
{

	/*
	$interval can be:
	yyyy - Number of full years
	q - Number of full quarters
	m - Number of full months
	y - Difference between day numbers
	(eg 1st Jan 2004 is "1", the first day. 2nd Feb 2003 is "33".
                 The datediff is "-32".)
	d - Number of full days
	w - Number of full weekdays
	ww - Number of full weeks
	h - Number of full hours
	n - Number of full minutes
	s - Number of full seconds (default)
	*/

	if (!$using_timestamps) {
		$datefrom = strtotime($datefrom, 0);
		$dateto = strtotime($dateto, 0);
	}
	$difference = $dateto - $datefrom; // Difference in seconds

	switch($interval) {
		case 'yyyy': // Number of full years
		$years_difference = floor($difference / 31536000);
		if (mktime(date("H", $datefrom),
                              date("i", $datefrom),
                              date("s", $datefrom),
                              date("n", $datefrom),
                              date("j", $datefrom),
                              date("Y", $datefrom)+$years_difference) > $dateto) {

		$years_difference--;
		}
		if (mktime(date("H", $dateto),
                              date("i", $dateto),
                              date("s", $dateto),
                              date("n", $dateto),
                              date("j", $dateto),
                              date("Y", $dateto)-($years_difference+1)) > $datefrom) {

		$years_difference++;
		}
		$datediff = $years_difference;
		break;

		case "q": // Number of full quarters
		$quarters_difference = floor($difference / 8035200);
		while (mktime(date("H", $datefrom),
                                   date("i", $datefrom),
                                   date("s", $datefrom),
                                   date("n", $datefrom)+($quarters_difference*3),
                                   date("j", $dateto),
                                   date("Y", $datefrom)) < $dateto) {

		$months_difference++;
		}
		$quarters_difference--;
		$datediff = $quarters_difference;
		break;

		case "m": // Number of full months
		$months_difference = floor($difference / 2678400);
		while (mktime(date("H", $datefrom),
                                   date("i", $datefrom),
                                   date("s", $datefrom),
                                   date("n", $datefrom)+($months_difference),
                                   date("j", $dateto), date("Y", $datefrom))  7)
                        { // Sunday
		$days_remainder--;
		}
		if ($odd_days > 6) { // Saturday
		$days_remainder--;
		}
		$datediff = ($weeks_difference * 5) + $days_remainder;
		break;

		case "ww": // Number of full weeks
		$datediff = floor($difference / 604800);
		break;

		case "h": // Number of full hours
		$datediff = floor($difference / 3600);
		break;

		case "n": // Number of full minutes
		$datediff = floor($difference / 60);
		break;

		default: // Number of full seconds (default)
		$datediff = $difference;
		break;
	}

	return $datediff;
}