Hi Sharon - we travel LGW to PFO three times a year and a good average time is about 4 hrs 35 minutes. It can take slightly less and has been known to take as long as 5 hrs 25 minutes (in January this year) - all depending on whether you are flying into head winds.
Thankyou so much for taking the time to respond. I am a very nervous flyer you see, so need to know how long it takes. Thankyou once again. I hope the Thomas Cook flight isn't too bad.