"Won" a book I didn't request?

Am I obligated to review a book if I didn't request it? Also, related but different; how long should a review take? I find sometimes I fly through books, but sometimes it takes a couple months to get through a book if it isn't captivating early on.
*sorry if this is answered in a FAQ somewhere, I recently joined and I haven't found that answer.

Is it possible that the publisher or author had multiple books in that giveaway and sent you the wrong one ?

I also tend to read books with some delay from the moment I purchased or obtained them, I don't think it is too much of a problem thought people who do review early and systematically might be at an advantage to obtain further books, and people with a history of missed reviews are explicitly said to lower their chances.

>1 Pepperwings: You aren't even obligated to write a review; not reviewing a book may affect your chances of winning an Early Reviewer book, but Member Giveaway is randomly assigned so not reviewing a book will never hurt your chances.

MG isn't regulated, but I recommend contacting lorannen if you truly did not request the book.