401(k) safe harbor plan has 2/28 plan year end. Employer today (12/2) states they want to switch to 12/31 year end for corporate and plan year purposes.

Assuming the written consents and other corporate documents are not completed until 12/4 or 12/5, is that too late for the notice period requirement. Normally, for a safe harbor plan, we would have given the notice by 12/1.

30 days is "deemed" to be reasonable notice, but is a 26 day period reasonable under these "relevant facts and circumstances?"

see Notice 98-52
Section X


A plan will fail to satisfy the ADP safe harbor or the ACP safe harbor for a plan year unless (i) the plan year is 12 months long or (ii) in the case of a new plan....

oops, you do not have a new plan. I am not sure how you are going to get around the 12 month rule. I don't recall seeing any transition relief for a plan that wants to switch plan years.

My understanding is that both the safe harbor contribution and ADP/ACP testing will be required for the short plan year unless the plan was amended timely to say that the plan would not be a safe harbor 401(k) plan for the short plan year (and then presumably would say that the plan would again become a safe harbor 401(k) plan for the first full plan year following the short plan year).