如果满足条件，PHP 将为变量分配新值

下面的代码中有什么更好的方法可以向变量添加新值$timestop并$time_diff是否满足条件？

//Calculates difference in time using 24h format
$timestart = strtotime("14:00:00");
$timestop = strtotime("07:00:00"); //if smaller value, it must end next day and meets the condition below
$time_diff = $timestop - $timestart; //elapsed time
if ($time_diff < 0 || $time_diff == 0) //if result is negative value, $timestop ends next day
{
   $timestop = strtotime( '+1 day' , strtotime("07:00:00") ); //+ 1 day changes timestamp
}
/* UPDATED */
$time_diff = $timestop - $timestart; //added again
echo $time_diff;