Sometimes you want to check if a string represents a valid timezone. Using PHP versions greater than 5.2, timezone_identifiers_list() could be a solution.

Take a look in the following function:

<?php
/**
 * Check if a string is a valid timezone
 *
 * timezone_identifiers_list() requires PHP >= 5.2
 *
 * @param string $timezone
 * @return bool
 */
function isValidTimezone($timezone) {
        return in_array($timezone, timezone_identifiers_list());
}
?>

References

From PHP manual

• timezone_identifiers_list() (PHP 5 >= 5.2.0)