One of the cornerstones of the Mindgasm challenge is to avoid classic masturbation.

The main reason is, that this heightens your sensitivity for subtle pleasure beyond your primary. 

There seems to be some confusion if ejaculations are considered a fail of the challenge.
Wet dreams are common.
Sex with a partner is mentioned
Some reach their first HFWOs (hands free wet orgasms). 

None of these ejaculations are a failure.
As long as you do not manually stimulate yourself and don’t watch porn, you are good.

Semen retention can help to increase your sensitivity, and it makes sense to limit ejaculations to the ‘absolute necessary’. But beyond a week or two, it doesn not really add much benefit.

So after the challenge, it makes sense to return to a more  sustainable rhythm, depending on your age that will range between 2 and 7 days. You won’t need pornography to arouse you, it will happen naturally, and you’ll know when it’s time.