I don't like to let a zip stall for more than an hour, but you'll find people that do things different ways. If it stalls for more than an hour, I usually finish the zip (only the shell in a thin line, starting from the hatchlings starting point) and place it back in the incubator so it can bust...
If it's zipping, it should be able to bust out of the egg if it gets around a good part of the egg. Sounds like you're going to have a duckling very soon❤️
Sounds like everything is good. Using your light, shine in the air cell and look for veins along the inside of the egg wall, especially thick veins. Is the bill clear from any membrane, and visible to you?
What is your humidity at? Do you have a small bright flashlight that you can candle with? If you're using the NR360, you usually have to turn the egg upright to candle, so that's why I suggest a small flashlight so you can candle with it laying down without picking it up
https://www.backyardchickens.com/articles/guide-to-assisted-hatching-for-all-poultry.72886/
This article is full of information and will help you decide if you need to step in or not. I always review the information before every hatch 😊 I wish you the best. Please share some pictures once it...