We are trying to decide whether to book a return flight to Washington D.C. at either 8:00 AM or 3:25 PM. out of Heathrow. The airport website says you need to be out there 3 hours ahead of time. When you factor in the time required to get to the airport from West Kensington, we would probably need to leave at 4:30 AM! Should we just go for the 3:25 PM departure time? Thanks for your input.