I had a similar experience. Mine said 66% after about 10 hours, but then the next morning it said 72. The temp is definitely off on it though, about 1.5 degrees lower than the glass veterinary thermometer.
I tested my little hygrometer/thermometer (that was sold for incubating, but I see on Amazon an identical one with a different label sold for use in instrument cases) with the salt water solution, and after about 10 hours it was reading 66%. The next morning it was still in the bag and read 72%...
