His mom doesn't want payment now. Why are you guys insisting that he ignore his mother's request to delay payment until next year? She might have a good reason for her request, or she might have no reason at all, but it is nobody else's business what she wants done with her money.

If she truly doesn't want the money until next year, put it in a CD. If you think you might need to withdraw the money before the year is out, put it in an interest bearing account that allows withdrawal at any time. Sounds to me as if you have already scoped out those options.