Pull Json Compare against PHP and Insert

Working on a project and came across someone else work that I wanted to try and combine with some json I have written up. What I am trying to do is may seem odd and you will have to bare with me.

I have the json being read like so (Basic Stuff)

$data = file_get_contents($url);
$array = json_decode($data, true);
foreach($array as $datatype) {
   echo $datatype["start"];
}

Within the json I have "start":"05\/02\/2020 1:00 PM", When I output it using the json_decode it displays as 05/02/2020 1:00 PM which is great, Works fine and dandy but what I am trying to do is compare this date format (Just the date not time) with a calendar written in php that someone else wrote.

<?php
$monthNames = Array("January", "February", "March", "April", "May", "June", "July", 
"August", "September", "October", "November", "December");
if (!isset($_REQUEST["month"])) $_REQUEST["month"] = date("n");
if (!isset($_REQUEST["year"])) $_REQUEST["year"] = date("Y");
$cMonth = $_REQUEST["month"];
$cYear = $_REQUEST["year"];
$prev_year = $cYear;
$next_year = $cYear;
$prev_month = $cMonth-1;
$next_month = $cMonth+1;
if ($prev_month == 0 ) {
    $prev_month = 12;
    $prev_year = $cYear - 1;
}
if ($next_month == 13 ) {
    $next_month = 1;
    $next_year = $cYear + 1;
}
?>
<table width="200">
<tr align="center">
<td bgcolor="#999999" style="color:#FFFFFF">
<table width="100%" cellspacing="0" cellpadding="0" border="1">
<tr>
<td width="50%" align="left"><a href="<?php echo "?month=". $prev_month . "&year=" . $prev_year; ?>" style="color:#FFFFFF">Previous</a></td>
<td width="50%" align="right"><a href="<?php echo "?month=". $next_month . "&year=" . $next_year; ?>" style="color:#FFFFFF">Next</a></td>
</tr>
</table>
</td>
</tr>
<tr>
<td align="center">
<table width="100%" cellpadding="2" cellspacing="2" border="1">
<tr align="center">
<td colspan="7" bgcolor="#999999" style="color:#FFFFFF"><strong><?php echo $monthNames[$cMonth-1].''.$cYear; ?></strong></td>
</tr>
<tr>
<th><strong>S</strong></th>
<th><strong>M</strong></th>
<th><strong>T</strong></th>
<th><strong>W</strong></th>
<th><strong>T</strong></th>
<th><strong>F</strong></th>
<th><strong>S</strong></th>
</tr>
<?php
$timestamp = mktime(0,0,0,$cMonth,1,$cYear);
$maxday = date("t",$timestamp);
$thismonth = getdate ($timestamp);
$startday = $thismonth['wday'];
for ($i=0; $i<($maxday+$startday); $i++) {
    if(($i % 7) == 0 ) echo "<tr>";
    if($i < $startday) echo "<td></td>";    
    else echo "<td align='center' valign='middle' height='20px'>". ($i - $startday + 1) . "</td>";
    if(($i % 7) == 6 ) echo "</tr>";
    echo $i - $startday + '1';
}
?>
</table>
</td>
</tr>
</table>

The goal is to compare the json start date with the correct day on the calendar. If they match then insert the "time" from the start into the calendars correct box along with the json value idnumber. Maybe it is the calendar I am using or maybe it is the way I was trying before but I kept getting all of the json data in every calendar box no matter the date.

Ideas anyone?