Example of converting between timezones using the DateTime and DateTimeZone classes.
Note that PHP will also take care of calculating relevant daylight savings!
<?php
$utc_timezone = new DateTimeZone("UTC");
$tallinn_timezone = new DateTimeZone("Europe/Tallinn");
// Create a new DateTime object in the UTC format
$datetime = new DateTime("2023-01-01 11:00:00", $utc_timezone);
// Convert the DateTime object to the timezone of Tallinn
$datetime->setTimezone($tallinn_timezone);
// Display the result in the YYYY-MM-DD HH:MM:SS format
echo $datetime->format('Y-m-d H:i:s');
// Returns: 2023-01-01 13:00:00
?>