ข้อสอบถามหาจำนวนวันระหว่างวัน 2023-10-18-2024-03-31 DateDiff code ไม่เท่ากันเพราะอะไรครับ

<?php  
	 function DateDiff($strDate1,$strDate2)
	 {
				return (strtotime($strDate2) - strtotime($strDate1))/  ( 60 * 60 * 24 );  // 1 day = 60*60*24
	 }
	 function TimeDiff($strTime1,$strTime2)
	 {
				return (strtotime($strTime2) - strtotime($strTime1))/  ( 60 * 60 ); // 1 Hour =  60*60
	 }
	 function DateTimeDiff($strDateTime1,$strDateTime2)
	 {
				return (strtotime($strDateTime2) - strtotime($strDateTime1))/  ( 60 * 60 ); // 1 Hour =  60*60
	 }

	 echo "Date Diff = ".DateDiff("2023-10-18","2024-03-31")."<br>";

	 $total_pen_day1 =  DateDiff("2023-10-18","2024-03-31");
	
	 echo $total_pen_day1."<br>";
	
?>