A team I was once on would take 2-4 days to estimate how much work we could get done in the next two months. We were usually pretty close! The important thing to understand here is that we had complete buy-in from Management. This was part of our process, and they understood that we needed that time to do a good job of estimation and risk management.

The problem in most organizations seems to be that no one is willing to absorb the cost of real estimation.