With a muscovy drake and mallard derived duck, 4 weeks to hatch. With a mallard derived drake and muscovy hen- 5 weeks.
I am raising some Pekin right now to cross with Muscovy. With a muscovy drake and a large breed mallard derived duck, the offspring will be similar in size (both large), with a muscovy mother, you will see a difference in sizes between the sexes.
I am raising mine for a faster growing meat bird. I have read that fertility is much lower in the hybrids and that they do best if raised together, without other muscovy females, from a very young age. I have 2 muscovy drakelings in with my 6 pekin (4-F and 2-M) they still kind of keep apart but they sleep together and haven't quite reached breeding age.
Do remember that the offspring will be infertile and the females will lay only very small eggs, which is the reason I think many don't breed them often, you put alot of work into 1 generation. Also, if you have pure breeds that you are wanting offspring from, keeping hybrdis with them can affect the fertility of the flock drake as he would be covering more females.