(PHP 5 >= 5.1.0, PHP 7)
Sets the default timezone used by all date/time functions in a script
bool date_default_timezone_set ( string $timezone_identifier )
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_WARNIN