The Legend of Zelda: Twilight Princess:

In four months, Aonuma's team managed to present realistic horseback riding,[l] which Nintendo later revealed to the public with a trailer at Electronic Entertainment Expo 2004. The game was scheduled to be released the next year, and was no longer a follow-up to The Wind Waker; a true sequel to it was released for the Nintendo DS in 2007, in the form of Phantom Hourglass. Miyamoto explained in interviews that the graphical style was chosen to satisfy demand, and that it better fit the theme of an older incarnation of Link. The game runs on a modified The Wind Waker engine.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". How long did it take to implement riding horses in a believable manner?
four