Sorry to hear this Chris
I know someone who had one and I think it was 6-7 weeks before they started to get back to normal, but its a slow process in the beginning and also how your Dad is affected by the surgery itself. Everyone is different.
I agree with George, go see your dad for as long as you can, at least if you are there for when he has the op or when he is due to come out of hospital you can help him when he may need you most. Also since he is in the US I believe the healthcare system is there to provide after care as well. Might depend on his cover though, also worth checking out.
I wish him well and a speedy recovery