Just for fun, let one go about July, after you just couldn't possibly eat any more zucchini. See how big it gets.
I had one a couple years back that produced a fruit, and the trunk of the plant laid on top of it, so I never knew it was there. For the life of me, I couldn't figure out why the plant quit producing fruit. When I finally pulled it out in October, there was a zucchini that was laying on the groung about 30" long, and 4" diameter at the base. All that plant's energy became dedicated to that one fruit....it was huge!