date_default_timezone_set

date_default_timezone_set() sets the default timezone used by all date/time functions.

Note:

Since PHP 5.1.0 (when the date/time functions were rewritten), every call to a date/time function will generate a E_NOTICE if the timezone isn't valid, and/or a E_WARNING message if using the system settings or the TZ environment variable.

Instead of using this function to set the default timezone in your script, you can also use the INI setting date.timezone to set the default timezone.

The timezone identifier, like UTC or Europe/Lisbon. The list of valid identifiers is available in the List of Supported Timezones.

This function returns FALSE if the timezone_identifier isn't valid, or TRUE otherwise.

Now throws E_WARNING rather than E_STRICT.

The function started to validate the timezone_identifier parameter.

<?php
date_default_timezone_set('America/Los_Angeles');

$script_tz = date_default_timezone_get();

if (strcmp($script_tz, ini_get('date.timezone'))){
    echo 'Script timezone differs from ini-set timezone.';
} else {
    echo 'Script timezone and ini-set timezone match.';
}
?>

date_default_timezone_get() -

List of Supported Timezones -