We are traveling in from the US and have an 8 hour layover before our Aer Lingus flight (arrive at 8, leave at 3:50). I have read that we need 1.5 hours to clear customs and check our bag in or on the next flight, 15 min. on Heathrow Express or 1 hour on tube. For the return, how early should we arrive for security (our flight is on a Friday at 3:50). By my calculations we only have about 3 hours in London. Worth it? Or should we just stay put or go to Windsor. Kids are older, would like to see the Eye or Buckingham Palace. Any suggestions?