Thanks for all the replies! Yes, I did find some great advise on the duck forum, and when I checked on the egg this morning, the pip was MUCH longer, so I guess it is finally zipping. Should I peel back the membrane? The duckling is trying to poke it's bill through, and there's no blood veins or anything in the membrane. Here's a picture from when it first pipped:
Sorry about the bad quality! The air hole was about the size of a grain of rice.
And here's a picture of the egg this morning:
You can see it's little bill! It's also chirping a few times every minute or so. So what should I do? Just leave it???