As I recall, there is a problem with the visualization of the transmitter in the GCS wizard if you don't have a flight mode switch.
The problem is only the visualization. The actual calibration works. If you make carefully sure that you move each control to it's limits and pretend that the visualization is working, it actually works.
@f5soh knows more about this, but I believe that this is an accurate description.
The slow windup is normal. It is trying harder and harder to be level, but it doesn't move because it is solidly on the ground. If it were free to move freely in the air, it would move a little with the small amount of motor difference, and the motors would stop increasing. So ignore this effect.