In order to get rid of the pesky warning in php about time zone, you can so one of two things: add call to the date_default_timezone_set on every file header, or, define it in your php.ini like this: date.timezone = US/Central, where the actual values relates to the server time zone.
Looking for you own time zone? not a problem. here are the php time zones.
And you can still use the date_default_timezone_set if you need to stray from the default timezone.