Straight from Google's site: Currently, it’s not possible to change the time zone of your reports. All reports for your AdSense account are based on United States Pacific Time (PT), and a day is considered to be 12:00am PT to 11:59pm PT.
This website http://wwp.greenwichmeantime.com/ and others say GMT doesn't go on DST, although the UK switches to BST (British Summer Time)...according to those websites PDT = GMT - 7 I'm so confused