I've always brined my swiss varieties for 12 hours. Even with my 4 and 5 gallon batches this seems to be plenty of time.
One thing that I've found is VERY important is to make your brine out of the whey you drained from the cheese.
This keeps the brine at the same PH as the cheese which stops any excessive drying, cracking or melting of the cheese wheel.
If your wheel comes out of the brine, very "elastic" feeling then you are well on your way to producing a cheese you can be very proud of. This is my favorite cheese to make since it is such a challenge to do correctly.
Good luck with this cheese and be sure to show us some pics once it's out of the press or brine.
It's a temperamental variety but the rewards of getting it right are out of this world.