Form 5330 for owner 401k at 12/31 - prior yr or current yr?

[TPApril]

One-person plan, employees are in a separate MEP.

Owner withholds the max 401(k) once a year on his 12/31 paycheck which is cut every year on 1/5.

The pay is included in wages for year ending 12/31.

Turns out owner forgot to deposit the 401k for 6 months.

Lost earnings was calculated and deposited

Perhaps this is a longshot but if the 401k is not going to be deposited until the next calendar year no matter what, for Form 5330 purposes can it be considered late for the next year, or more likely since it is included in taxes for prior year filing, does it have to be in that year's 5330?