获取今日的开始和结束时间戳

 $t = time();
        //今日开始时间戳
        $start = mktime(0,0,0,date("m",$t),date("d",$t),date("Y",$t));
        //今日结束时间戳
        $end = mktime(23,59,59,date("m",$t),date("d",$t),date("Y",$t));