//$startdate是开始时间,$enddate是结束时间
<?php
$startdate="2018-04-13 00:00:00";
$enddate="2018-04-14 00:00:00";
$date=floor((strtotime($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";
?>