Do I buy a house? What about sex?

[Dom R]

I have found that most people, if unfamiliar with the MB concepts, actually agree that it is an unreasonable amount of time. (?!?)

yeah, I understand that. but the point is, he wasn't willing to commit to ANY time, right?

Your mother in law should know that, in the face of the lies her son is telling her about how he tried so hard, blah blah blah.
You sound like you actually have a positive relation with your MIL. She sounds like she would believe you. which could make a difference. It may not be "THE" difference, but many small nudges from different areas, may together keep him rolling in the positive direction.