The settable timings are related to the abstract sequences that are NOT tied to an animation.
During boarding/deboarding, the luggage animation is fixed, what you can set is the parallel non-visible passenger deboarding. Same for refueling, since there's no actual animation for it, what you can specify is the time taken by the process which is not shown as animation.
Since catering doesn't have a non-visible process with an arbitrary length, but IT IS the animation, you can't set the timing freely, just like all the other visible animations.