Join Date: Oct 2006
Location: London, UK
Programs: BA Gold, VS Silver, SQ Silver, IHG Plat Amb, Hilton Gold, Marriott Plat, Accor Silver, Radisson Prem
Posts: 16,871
As arrivals and departures are separated at LHR, you won't have access to any lounges on arrival. The Galleries Arrivals lounge (which is landside) closes at 14:00, so you won't be able to use that.
On departure the next day, as your flight is after 06:00, you will only be able to use the Galleries Club lounges due to your onward flight being in business class. You could use the Concorde Room on a same day connection, or for flights departing before 06:00 (of which there aren't any from T5).