Keep in mind that the line to get into ICE could be very long. Unless you are a guest of the hotel, you must wait on the general public line. It can be long. That said, it is incredible to see. You walk through different holiday scenes that are floor on up made, made of ice. There are ice slides for the kids. After you go through the cold part, you can stop at the cafe for a warm hot chocolate, and have a look around the rest of the hotel, which is itself something amazing to see.
So, to answer your question, I would set aside a couple of hours (line to get in, actual attraction, walking around hotel/hot chocolate) for the side trip. The hotel is located just outside of Disney World. If you are driving, it is two minutes outside of Disney World.