You had some time but not a lot of time. Dean would be occupied for a while with the sliver. You quickly look over the Chronivac to see what you can do.
Dean had always been average but you saw a way that you could make him more than average. You could turn Dean into a stallion but you wanted the change to be slow, very slow. You decided that it should take thirty days, a whole month, before Dean became 100% stallion. You set it so that every hour, a very small change would occur to Dean to make him more stallion like but he would still be mostly human for the first half of the month: 10% stallion after three days, 20% stallion after six days, and so on.
You clicked on mental changes as well although you chose to preserve Dean as Dean throughout the whole transformation, you wanted him to act a little more like a horse each day. He wouldn't adopt a horse identity, just a horses behavior patterns. In fact, you set it so that even at 100% stallion, Dean would be a talking stallion and still your friend.
Physically, you set it so that Dean would simply bulk up first, not getting any animal parts until next week but certainly becoming more muscular before then.
Finally, you set it so that everyone except you would think everything was normal. At whatever stage of part human part stallion Dean was, everyone would assume that he'd always been that way. Memories and reality would adjust accordingly.
Then you closed the Chronivac because you could hear that Dean was done and on his way back. When he came back, you immediately noticed his hair. He did not have a mohawk or a horses mane. A horses main would be too big of a change at a rate of only 0.139 percent change per hour. But Dean's hair was noticeably thicker and more wiry. It was also brighter in color moving toward a sorrel chestnut color.
You tell Dean, "Let's go out tonight. I have a feeling you'll be more popular with women tonight."
When you set the memory adjustment, you didn't want the Chronivac to replace any memories. Dean would not suddenly have memories of being more popular with women. He would just remember having always had bright, distinctive hair and still think he'd never been this popular in the past.
Dean asked, "Why? What makes tonight any different from any other night? Why would any woman even notice me?"