28 days for standard ducka is when they should start hatching. It should be 45-55% Humidity during incubation and 65% or more during Hatching
Mallard-derived ducks are 28 days average, muscovies 35 days, call ducks 26 days. Humidity depends somewhat on local factors, but 25-35% up to the last 3 days and 60-70% for the last 3 days usually works for most folks. 99-100 degrees for incubators with fans, 101-102 without a fan.