With big goose eggs often you can tell at 4 days if you know what to look for. By day 7 you can see the veins for sure. By day 10 you are 1/3 of the way there and can see the embryo moving.
It is grey and gloomy and raining here. I went up to check on my babies in the brooder and had to add water to my incubator with the goose eggs. I ran the light over the grey dewlap and BOTH have veins today!