Hi Fiona, they are very flexible about check in
Officially 2pm but arrive when you can and they can either stash your luggage while you wander off for a while (try the Wallace Collection nearby) or call in advance and they may be able to accommodate you - especially if the previous users of your room have left early.
They try to give you a room as soon as possible but checkout is eleven am and they need time to clean. If you are just off an overnight flight from the US, why not have breakfast (pricey but good) and catch up on email in the lounge. Timing is unpredictable but you can get lucky too.
Check-in time is 2 pm, but you can request an early check-in. They are typically accommodating when they can be.
Check in time is 2:00PM, Check out is 12:00 noon
Get an answer from Durrants Hotel staff and past guests.