Duck eggs take 28 days to incubate, unless they are muscovy eggs, in which case it is (I believe) 35 days. If you post pics of the eggs, we can probably tell you if they are duck or chicken. Duck eggs also need higher humidity, so it would be very helpful for you to know. Out of curiosity, why did you decide to take the eggs? Muscovies are known to be great broodies, so I probably would just have left the eggs with mama. But I'm sure you had a good reason, I'm just wondering.
If you can't post pics or if no one here can tell what they are, you *may* be able to tell whether they are duck or chicken by how quickly they mature. A chicken egg can reliably be candled at 5 days and see a definite embryo, often swimming & moving around. Duck eggs reach that same stage at 7 days. However, if you don't have much experience candling then you will be hard pressed to tell. By day 18, chicken embryos will nearly fill the entire egg. Duck embryos won't fill the whole egg until around day 25 (later for muscovies). But again, without some experience to judge with, you'll have a hard time telling.
Worst case scenario, you wait until day 18--lockdown for a few days (chicken lockdown humidity won't hurt duck eggs)--if they hatch around the 21st day, they're chickens (duh). If not, put them back in the turner until Day 25 (or Day 30, I think, for muscovies) and lock down again at that point.
Of course, this is all assuming that they hadn't already begun to develop under the broody duck... in which case the time estimates will all be completely wrong.
Anyway... wish I could be more help. Pics would be a great idea if you can get them. Good luck!
I know that sounds bad. I should know this. Let me explain though....I caught my muscovy hen going into this nest and saw her on it with the drake standing guard. But the eggs don't look much bigger than chicken eggs? Anyways those were put in the 8th. Which me luck.
