We didn't make a reservation 24 hours in advance. Our TD, Scott, made the arrangements 4 or so hours in advance. I'd suggest either asking the concierge or TD to help with this as soon as you get to Beijing to avoid disappointment if it happens to be a busy time.
As always, Portolan, thanks for the tip. Shescha, thanks for your input.
I have a question. I've looked at some reviews on the internet from both places and I noticed that they encouraged people to "reserve" the duck 24 hrs. before. It that true? Thanks for your input.