He was diagnosed with heart failure just before the games. Friedman stepped in on very late notice, and aside from the disastrous 15 minutes, I think actually equated himself pretty well doing a couple tough sports on short notice.
It was only announced a week before the Olympics. Not sure how much warning they had before that, but given they had went forward with all the announcements like this with Armitage included, I don't imagine it was more than a week or two tops