When must a beneficiary decide her minimum distribution?

[Peter Gulia]

A § 401(a)-(k) plan’s only participant dies without having begun a distribution, and before the plan, following Internal Revenue Code § 401(a)(9), required a distribution.

Assume the plan allows a beneficiary the widest possible choices about a distribution, with no more constraint than is necessary to meet § 401(a)(9) rules.

The participant had no spouse.

The participant’s beneficiary is not an eligible designated beneficiary.

The participant’s death was September 17, 2025.

Assume all possibly relevant years are the calendar year.

What is the latest date for the beneficiary to specify to the plan’s administrator any choices the beneficiary might make regarding the form of a distribution and when it begins?

What is the latest date a plan’s administrator may wait until, absent the beneficiary’s choice, one must impose the plan’s default minimum distribution?

I imagine I could sort this out by reading the tax law regulations, but I’m hoping a BenefitsLink neighbor can save me some time. Thanks.