Date time stuff.

date_time_stuff.php

<?php
function time_zone_offset_to_identifier(string $offset, int $offsetIndex = 0) {
   static $timeZoneOffsets = [];
   if (empty($timeZoneOffsets)) {
      foreach(timezone_identifiers_list() as $timeZoneIdentifier) {
         $dateTimeZone = new DateTimeZone($timeZoneIdentifier);
         $dateTime     = new DateTime('NOW', $dateTimeZone);
         $timeZoneOffsets[$dateTimeZone->getOffset($dateTime)][] = $timeZoneIdentifier;
      }
   }

   $dateTimeZone = new DateTimeZone($offset);
   $dateTime     = new DateTime('NOW', $dateTimeZone);
   $dateTimeOffset = $dateTime->getOffset();
   foreach ($timeZoneOffsets as $offset => $offsets) {
      if ($offset == $dateTimeOffset) {
         return isset($offsets[$offsetIndex])
            ? $offsets[$offsetIndex] : $offsets[0];
      }
   }

   return null;
}

$id = time_zone_offset_to_identifier('+02:00');
print $id; // Africa/Blantyre

$id = time_zone_offset_to_identifier('+02:00', 100000000);
print $id; // Africa/Blantyre

$id = time_zone_offset_to_identifier('+02:00', 25);
print $id; // Europe/Istanbul