Saving squash seeds?

(notice the followup header to r.g.e.)
How mature does a squash need to be for you to sucessfully save the seeds? I let a volunteer squash vine grow in my garden this year (actually I transplanted it from a path to a big bed where it could run) and it turned out to be an odd variety that I've never grown before but like very much. It's probably a cross between a Tatume that I grew a few years ago and a yellow straightneck or crookneck. The vines run and branch like a pumpkin vine (like the Tatume), but stay relatively short.
While I was out of town for 3 weeks, it set its first few fruits, and I picked the big hard-shelled squash when I got back. The seeds are full-sized, but the shell of the squash was still soft enough I could scratch it with my thumbnail, barely. The plant has started bearing good again, and I don't really want to let another fruit mature on the vine and have the plant shut down again.
I still have one of those 4 big fruits that I haven't cut yet if the seeds will continue to ripen off the vine fruit. It has been sitting on the kitchen counter for 2 weeks and shows no signs of rotting, if that's any indication how mature it is.
I suppose I could test the germination of the seeds that I saved, but I don't know if they need a few months dormancy before they will sprout.
Thanks, regards, Bob
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