Muscovies lay and brood when Muscovies want to, it seems. Just mark the calendar when they start to sit and stick. (stick to the nest, stay there). They like big nests, at least 8, a dozen even more.
One of my girls just set a hugh pile of eggs from the 5 of them that have layed in that nest for a week. So the new nest they are starting.... No No No. I will collect those eggs. One hatch at a time around here is all I want to deal with.
I am hoping for a Xmas hatch. Pea soup, finely chopped Romaine and coarse ground mixed seeds along with chick starter will be waiting for them. Little dishes are cleaned, stacked and ready to go. Have to put the game camera back in the duck house yet though.
Oh, almost forgot, they wait until they have enough eggs (that they consider enough eggs) before they start to sit. You may see her sit on the eggs for awhile then get up and leave for the day. She's just turning them. Once she sits, she will stay on the eggs and only get off to eat and drink maybe bath in the beginning. That's when you mark the calendar. It is important that she have water to bath in close to the hatch date. I have seen my ducks just walk through their pool and get just their bellies a little wet during the brooding period. But when it is time for them to hatch they will bath, submerge completely, barely shaking off water and go back and sit the eggs. Then you know. You have 3 days to get everything ready for them. That is when I take the drake and other hens but 1 out. I leave her friend in to help her protect the babies if need be. I love watching how they prepare themselves and adjust the humidity with their bathing and sunbathing. Its different all the time. There is no way we can do what they do with the incubators.
When sitting, make sure they have a lot of good food at hand, they will only eat once a day. My ducks get equal feed and scratch free choice. Your duck will loose weight while sitting a nest, that's normal. After the hatch, I feed her high protein to get the weight back on fast, again free choice. Pea soup and scrambled eggs help in that and is really appreciated by the Duck and her babies. The babies dishes I water down more than her bigger dish. My momma ducks lead them to the pea soup before the feed, so keep that in mind. Actually its always pea soup, ground seeds, then feed. A few days later she leads them to the chopped Romaine and scrambled eggs fits in there somewhere. I don't remember when or where.
Hope this helps, enjoy your hatch that I am sure is coming.