This maybe just urban legend;
I have heard of duck & geese owners in particular that had eggs actually freeze and crack before the female started incubating. (it was Not April 1, when this statement was made). The frozen eggs went on to hatch according to their testimonials.
I was skeptical...
It depends on the pair. Some start incubating the first egg from the get go. Others tend to stand over it and do not start incubating until the second egg arrives. I also have eggs not hatch until the 23 day or even later. Ambient temperature also plays a factor I am thinking.
Speaking from " MY EXPERIENCE" my birds have produced every possible combination. I have noticed the pattern is" There is NO PATTERN" outside of the fact they usually hatch in 19 days