How long does it take to write a picture book?

 I love telling how long it took to write my first published picture book.

 It took 20 minutes. (and my husband tried to tell me something and I kept saying, wait. just wait. I've got to get it down. When I finished it, he said, "Did you know that eggs will explode in the microwave?" yes, then I had to go clean up the microwave.) 

But wait -- it then took several years of REVISiON. So , did it take 20 minutes, or 3-4 years?