Sometimes I have left them for up to seven days without noticing any growth. There are knowledgeable mushroomers that would also argue that while morels increase in size, it is not true growth. And I shouldn't argue this point because I don't understand their belief. I do not agree. I believe that if you could dehydrate a morel that's an inch tall and then could somehow dehydrate the same morel when it was five inches tall you would have more mushroom in both size and weight.
Dehydration removes all the moisture.
It's a combination of moisture, temperature, and someone with enough patience to not collect it for the dinner table. You may not notice the mushroom in photo 1 at first glance. It's only about an inch and a half tall and is grey in color. It is right in the middle of the picture. In photo 2, after six days the mushroom has increased to about three and a half inches in height and its color is more of a yellow-grey.