How is rise/fall time definition
There is an accepted definition for how to calculate settling time such that the waveform has reached the final value within a desired tolerance.
https://en.wikipedia.org/wiki/Settling_time

So, after the settling time, the waveform is at 100% +/- the tolerance.

In reality, of course, you take VDDD to be 100% and 0V to be 0% (or whatever is suitable for the type of output you're looking at).