php取当天的0点和23点59分59秒的时间戳方法

$year = date("Y");
$month = date("m");
$day = date("d");
$start = mktime(0,0,0,$month,$day,$year);//当天开始时间戳
$end= mktime(23,59,59,$month,$day,$year);//当天结束时间戳