Just got a notice from Virgin Altlantic that the flight times for our flights home in June have changed. Both the flight from EDI to LHR and LHR to San Francisco have changed. We now have 1 hr 40 min to get from LHR terminal 1 to LHR terminal 3. Assuming the flight from EDI isn't late, do we have enough time? Do we need to go through customs at LHR or when we land in SF?