The Quickness (qu) option, in %, controls the speed of response to a request to change the pitch. All hat rises, hat falls, and stress rises can be thought of as suddenly applied commands to change the pitch, but the larynx is sluggish and responds only gradually to each command. A smaller larynx typically responds more quickly, so while Harry has a quickness value of 10, Kit has a value of 50.
In engineering terms, a value of 10 implies a time constant (time to get to 70% of a suddenly applied step target) of about 100 ms. A value of 90% corresponds to a time constant of about 50 ms. Lower quickness values may mean that the f0 never reaches the target value before a new command comes along to change the target.