10am-11.30pm Cost 3.00 per half hour. Alas the machines weren't available until 11am the day I visited them, but I shared a pot of Lapsang Souchong with my wife and a friend. Their Pu'erh tea was reasonable though, so maybe I should have. This will leave some room in your schedule for looking at book stores. For extras you can visit the Irish shop near Drurys and sample some Irish teas.
Some supermarkets seem to have decents teas too, so have a look.
The ever-popular tea department offers forty varieties in green or red tins, including Darjeeling, Assam, Ceylon, Formosa and China teas as well as the famous blends named Royal, Crown, Celebration,Breakfast, Fortmason, New York, Queen Anne, et cetera. Prince Charles reportedly prefers the Pushkin blend with its aroma of bergamot and other citrus flavors. The tea department is on the 4. floor and offers several superb Darjeeling teas. It is in the Docklands area of London, right next to the Design Museum. It is a somewhat informal museum, with a very hospitable staff.