The ones in his butt that I had removed, I left the stitches in for about 10 days (per vet's orders). After that, it was just a couple of weeks for the scabbed places to completely heal up. However, vet did say that if he was unable to stitch one of them due to a lack of extra skin (as it will be with the ones next to be removed) then it would have to heal as an open wound. It would take longer and leave a bigger scar than the ones with the stitches did.
For what it's worth, since I have been through it once already, here is some pictures of my guy's melanomas...before and after. The surgery took a little over an hour and was pretty much completely uneventful as both the melanomas were only skin-thickness and it was just a matter of cutting away the skin they were growing on.
You can see the smaller one 2 or 3 inches to the left of his butt crack and the other, larger one is to the right of it, almost in the middle of his crack.
Here, we had just gotten back from the vet after they were removed.
Here is the day after the stitches were taken out.
Now, he's got a bit of a scar where the far left one was, but it's not terribly noticeable. I don't really have any current pics that show it well.
And here are the 2 that are currently growing on his face that will be removed this winter, along with the one on his back that I don't have a good picture of.