Here's the full quote from SFX:
Martin says heís knuckling under with THE WINDS OF WINTER. As for a deadline he shakes his head and only offers, "I've given up making any predictions after my experience with A DANCE WITH DRAGONS as they just bite me on the ass. I'll just write as fast as I can, make it as good as I can, a page and a word at a time, and eventually it will be done."
He does admit to feeling a twing more pressure now with the TV series gaining on him. "I hope they make Book 3 into two seasons. I think Books 4 and 5 will have to be two seasons each as well, so that gives me four years to finish," he laughs. "But really thatís something I have to disregard. Part of the struggle with A DANCE WITH DRAGONS, or even A FEAST FOR CROWS before it, is when I become too conscious of the book being late or a deadline approaching it just slows me down further, if it doesn't stop me all together, so suddenly I'm worried about the big picture. It's soul-destroying and you have to forget the external world, or at least that I have to. You have to put yourself in Westeros and say, 'Here I am on a battlefield, and Iím Tyrion now. How would he say that?' And eventually the whole story will be done that way."
I don't know he arrives at the four-year estimate if he's banking on the third, fourth and fifth books each being split into two seasons. That would give him considerably longer - unless he thinks HBO will start airing more than one season per year. Anyway, I don't think Feast
will get two seasons each, or at least not without the producers reshaping the material to a very significant degree.