Note: It was free for Kindle when I downloaded it and is quite a short book, but does let you know the difference of types of tea and how long to brew along with recipes.
More info. about afternoon tea and customs here
I found an interesting article on tea etiquette at Huffington Post
High Tea or Low Tea?
There is some confusion over high tea and low tea. High tea is served on a dinner table usually between 6 and 7 p.m. Low tea or afternoon tea, is served around 3:00 - 4:00 p.m. on a lower table (coffee table height) in a living room/drawing room.
Note: napkins are never put on the table once they have been on your lap (folded at a diagonal). If you need to leave your chair, your napkin should be placed on your chair until you return.
Lots of info. about tea etiquette here
