I'm a bit confused about the use of 'GMT' and the footnote - I assume that the time is fixed based on local time in San Francisco, and you are converting this to UK time based on the 'normal' time difference (8 hours). If that is the case, it would probably be clearer to change 'GMT' to 'UK time', with a footnote stating this can vary by 1 hour due to differing summer time dates. Or if you want to be strictly accurate just state the San Francisco local time with the 'normal' UK time below.