Plan Termination Notice/Timing Requirements

I know for PBGC covered DB plans, you must give notice to the participants 60-90 days before plan termination.  For Safe Harbor plans, you must give notice 30 days before plan termination.  Are there any requirements to notify the participants in profit sharing plans or non-PBGC covered DB plans?  Do you have to give 15 days notice before plan termination, or can we make the termination date the same day we are preparing the amendment in these cases?

For non-PBGC DBPs, if the plan is not already frozen then you need to provide 15-day advance notice (ERISA 204(h) notice) of an amendment that results in a reduction in the rate of future accruals. 

The 204(h) notice applies to all DB plans, plus DC plans that are subject to IRC 412, such as money purchase plans (but not profit sharing plans).

The notice has to be given 15 days in advance for small plans, but 45 days in advance for large plans. There are some exceptions in cases of mergers and acquisitions - the rules are in 54.4980F-1.

https://www.ecfr.gov/current/title-26/chapter-I/subchapter-D/part-54/section-54.4980F-1