Jeff decides to choose the donkey, and chose 24 hours for his transformation to last.
The following screen asked how long the transformation should take. The rule is, the timer for how long it will last before turning you back to human again, does not start until you are a full donkey in body.
For instance, if you choose the transformation to take 24 hours to fully complete, the timer that says how long it will last, will not begin until the 24 hour tf to completion ends.
The options are the same as the previous stage, except it adds the "instantaneous" option:
Instantaneous
24 hours
7 days
30 days
A year
A decade