Thank you for your suggestion Globaliser. We are returning to California via United Airlines which as you may know, operates from Terminal 2. We've booked a room at the Hilton Garden Inn Heathrow, adjacent to Terminals 2 and 3, and are hopeful that will ensure a smooth transfer on the day of our flight. While your recommendation intrigues me, I do not believe my traveling companions will go for it, and frankly, we have found the London trains to be only slightly more reliable than those here in the U.S., thus I believe we will stay with our plan to wake up at the airport.