PHP得到某段时间区间的时间戳 php定时任务

$y=date("Y",time()); 
$m=date("m",time()); 
$d=date("d",time()); 
$start_time = mktime(9, 0, 0, $m, $d ,$y); 
$end_time = mktime(19, 0, 0, $m, $d ,$y); 

$time = time(); 
if($time >= $start_time && $time <= $end_time) 
{ 
// do something.... 
}