Here's a link to the interview in Powell's, and an excerpt:
Jeremy [Garber]: I suspect most readers are unaware of the translation process. I've read elsewhere that you proceed page by page. Is that your general method of working?
[Natasha] Wimmer: I usually do between five and ten pages a day. I do a quick translation in the afternoon of, say, five pages, and the next morning I revise. Working that way, I make my way through the book, and then at the end I spend a pretty long time going back over the whole thing and revising it again.
Here are a few other interviews with Wimmer: New York Times, The Quarterly Conversation, New York Magazine.