//mktime = mktime($hours,minute,seconds,month,day,years)
$start_time = mktime(0,0,0,01,09,2010); //开始时间
$end_time = mktime(0,0,0,02,09,2010); //结束时间
$times = $end_time-$start_time; //开始与结束之间相差多少秒
$now_time = $times/(24*3600); //得出一共有多少
mktime得到的是秒为单位哦