Error Strict Standards: strtotime() ...

[wakh]

GS 3.3.1a Beta / Bleeding Edge

get error (warning) on page which using plugin "guestbook"

Code:

Strict Standards: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/Moscow' for 'MSK/4.0/no DST' instead in /var/www/u4978547/data/www/planeta-cars.ru/admin/inc/basic.php on line 336
...
Strict Standards: date() [function.date]: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/Moscow' for 'MSK/4.0/no DST' instead in /var/www/u4978547/data/www/planeta-cars.ru/admin/inc/basic.php on line 336

totally 8 warnings

how to fix it?