It is not safe to rely on the system's timezone

It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting 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 'Asia/Krasnoyarsk' for '7.0/no DST' instead in C:\xampp\htdocs\bookstore\administrator\components\com_virtuemart\classes\ps_main.php on line 880

Answer :
Check php.ini then find
[Date]
; Defines the default timezone used by the date functions
; http://php.net/date.timezone
;date.timezone =
;php_value date.timezone Asia/Krasnoyarsk

date.timezone = "Asia/Krasnoyarsk"