Muscovy are usually much more seasonal in their laying than mallard derived breeds. Usually 4-6 months but if they are not at that age in spring or early summer they are likely to not start laying until the following spring.
A lot depends on where you live. If you have harsh winters, don't expect laying until spring. If you have mild winters than they could begin laying this year.
I live in north Alabama. Last year I had ducks hatched around March that began laying occasionally in September. One went broody in October ( I DON'T recommend allowing that though) and I had ducklings hatch in December, then January and March. We got snow and below freezing temps during the first broody's time on the nest. So, a lot is up to them. Out of those hatches, I had 1 go broody and 1 or 2 lay for a bit but that is it and they have stopped for a few weeks now.