To close this out, I ended up talking with Turbo Tax support. That was a very nice experience. Since the house was not rented in 2018 at all, the thing to do is put 0 days for how many days rented and 0 days for how many personal days. When they are both 0, it is happy. Since it was not rented that year, it doesn't need the personal days for any calculations of personal vs rental use. After that, no issues.
Thanks to everyone for their answers and the way to get to support.
