Breeding wool into a hair sheep?

I have some work/hair crosses. For example I will use our st.croix/jacobs ewe.
We are going to purchase some tunis ewes and an unrelated tunis ram. We aren't worried about keeping a completely tunis flock, but we would like a generally uniform one. So if I were to breed the st.crox/jacobs ewe with a tunis ram, how long down her line would I have to go until her offsprings offspring started looking more like a tunis? Im assuming this is probably different for every animal, but in general how long?
Thanks!

I don't know how long it would take to make the offspring look Tunis (probably at least two or three), but if you plan to use the wool, it will take several generations of careful breeding to get all the kemp out of the wool.  We've had Merino/Shetland crosses.  The Shetland parents were good quality and only had kemp on their legs, not up in the wool, but the crosses had kemp on their whole hindquarters for at least two generations (as far as we went with them).

I crossed hair sheep with wool sheep...ONCE!

It was not a great cross, but my sheep shearer said if I ever did that again she would slice my throat with her sheep shearing clippers. I am pretty sure she was serious.

It will take at least 4 off spring to get the look you are after, but still might have recessive genes in your flock a LONGGGGG time later. I still have a few exhibit hair-wool type fleeces on occasion for my mistake. Do as you wish of course, but honestly I consider what I did as a mistake.

How long? Numerous generations along with active selection/culling. I want hair sheep. I was given a few hair/wooly cross ewes. They and their daughters and granddaughters have been bred to hair rams. I still get wool sometimes mixed in with the hair coat, which means that they are more susceptible to flystrike and tend to retain a mat on their back after shedding....which I have to shear off. Gradually  I'm eliminating them from the flock. The mixes aren't worth dealing with, as far as I'm concerned. But at least they convert grass into meat, and one by one they go for slaughter.