//當天開始時間
 $start_time=strtotime(date("Y-m-d",time()));
 //當天結束之間
 $end_time=$start_time+60*60*24;
 echo  $start_time;      1541001600
 echo $end_time;        1541088000
 $start_time=date("Y-m-d H:i:s",$start_time);       
 $end_time=date("Y-m-d H:i:s",$end_time);           
 echo  $start_time;      1541001600        //2018-11-01 00:00:00
 echo $end_time;         1541088000       //2018-11-02 00:00:00