Entry "immediately" upon meeting service requirements - day of or day after?

If a plan provides that an employee will become a participant eligible to receive employer contributions "immediately" upon meeting the eligibility requirements, and the eligibility requirement is 2 eligibility computation periods in which he completes 1,000 hours of service, does the employee enter the plan on the last day of the second eligibility computation period, or the day after? 

In this situation the eligibility computation period is the 12-month period beginning on date of hire and then switches to plan year.  Date of hire is 1/1/2022 and plan year is calendar year. So eligibility computation periods are 1/1/22 - 12/31/22 and 1/1/23 - 12/31/23.  Does the employee become a participant on 12/31/23 or 1/1/24?   

I have generally interpreted similar terms to mean that the day has to be completed for the eligibility period to be completed, meaning the ECP ends at 11:59 on 12/31/23 and then the employee becomes a participant immediately at 12:00 am on 1/1/24. But the TPA's interpretation is the employee became a participant on 12/31/23.  

This is a money purchase plan, if that's relevant, and the issue is whether the participant should have received a contribution based on his compensation for the day of 12/31/23.

Just had a similar conversation. 

As I noted in that thread I would say a person hired met the requirement on 12/31.   We have plans here that say once you work 1,000 and 12 mo they enter back on the 1/1 of the calendar year they meet the requirement.  We have people who are hired on 1/1/2023 we would have them enter on 1/1/2023.  

There is a difference between fulfilling the plan's eligibility requirements and the plan's entry date.  The plan should specify all the rules needed to determine when the individual starts participating in the plan.  If the plan says the entry date is immediate upon fulfillment of the eligibility requirements, then there is an argument that this participant became a participant on 12/31/2023.  If the plan definition of compensation is compensation earned while a participant, then the participant will have 1 day of compensation.

Best practice would be to clarify in the plan document the definition of the Entry Date.