I think they should be laying soon. Muscovys are good at hiding their nests. They could already be laying and you just don't know it. Don't know about the weather in Alaska though. They might wait until spring.
OK I did a search on the Muscovy duck forum and they say 6 to 7 months, so you 're a couple of months early. I know my males hatched in April are fertile because I see movement in their eggs. They were laid about three weeks ago but my female is over a year old.