//$startdate是开始时间，$enddate是结束时间
<?php
$startdate="2011-3-15 11:50:00";
 
$enddate="2012-12-12 12:12:12";
 
$date=floor((strtotime($enddate)-strtotime($startdate))/86400);
echo "相差天数：".$date."天<br/><br/>";
 
$hour=floor((strtotime($enddate)-strtotime($startdate))%86400/3600);
echo "相差小时数：".$hour."小时<br/><br/>";
 
$minute=floor((strtotime($enddate)-strtotime($startdate))%86400/60);
echo "相差分钟数：".$minute."分钟<br/><br/>";
 
$second=floor((strtotime($enddate)-strtotime($startdate))%86400%60);
echo "相差秒数：".$second."秒";
?>

PHP中计算两个时间相差的天数、小时数、分钟数、秒数