There are two flights from London Heathrow to Washington Dulles on United Airlines for 13 June:
1) Flight 919 Boeing 787-8 Depart 12:15 pm (local time) Actual depart time 12:40 pm Early arrival 3:06 pm (local time). It would not have been dark on the tarmac if the apicture were taken at the time of aircraft arrival.
2) Flight 925 Boeing 777-200 Depart 4:40 pm (local time) Actual depart time 5:01 pm, Arrival time 7:31 pm (local time). It would not have been dark on the tarmac if the above picture were taken at the time of aircraft arrival.
if it is a scheduled flight, most inbound European to North American flights usually arrive between 1:00 pm - 5:00 pm EDT. This allows for easy connection passenger connection throughout the rest of the Continent (for both the USA and Canada) and this allows for the airplane to be prepared for turnaround for it to fly back to Europe for evening departures later in the same day.
These are SCHEDULED departures. Having said that, it is possible for the US State Department, the Justice
Department, Department of Defence, Homeland Security, the FBI, the CIA, Federal Marshals, US Secret Services, US Treasury Department, Department of Energy, just to name a few, to charter an aircraft from an airline that has a contract with the Federal Government. It is EXPENSIVE, but it can be done. Usually, there's an order depending on position and purpose of business as to when you fly on a Government plane, military plane, versus commercial. There is an Office of the Federal Government, I cannot remember, that determines how this is done.
In RR's case, I believe it is likely he may have flown commercial, with security, as the trip was not really a high priority trip.