The Pacific Time Zone has 'summer time' (a.k.a. 'daylight saving time) in the same way that the UK has.
For most of the winter 10am (PST) = 6pm (GMT).
For most of the summer 10am (PDT, Pacific Daylight Time) = 6pm (BST)
However clocks are put forward and back on different dates in the Pacific Time Zone from those here in the UK. So for two weeks in March (when American clocks have gone forward but ours haven't) 10am (PDT) = 5pm (BST). The same applies for 1 week around the beginning of November.
Chris