I have muscoveys and some of my girls have never laid an egg and some not for a long time.
Mine start at 4 months or 5 months. Sometimes the first eggs of a beginner are a bit smaller but when they go through their first moult they begin to lay normal sized eggs.
You don't have to do anything about the egg laying. Just collect..cook and enjoy. Great for baking cakes, biscuits etc.
I love to fry sunny side up. Great in omelettes too.
You will know when a duck goes clucky, she will stay on the nest and when off and walking she will squeak and fan her tail out. She will also line the nest with feathers.
Your ducks I have never had anything to do with, I have only had muscovey ducks.