It really depends on how quickly your horse heals up. I had a horse that I had a couple of Melanomas taken off of this spring. They were pretty good sized wounds but the stitches came out 10 days after and about 2 weeks after that, he was completely healed up. But I started using him again as soon as the stitches came out. It also depends on how big the wound is to begin with.
I am wishing him luck in his surgery though, I know how scary even minor surgery can be.