Traditional 401(k) plan to Safe Harbor 401(k) plan

Have an on-going traditional 401(k) plan (calendar year) can it be changed to a safe harbor 401(k) plan (with SHNE contributions) effective for this 2024 calendar year or do we need to wait until 2025?

Thanks.

You have until 11/30/2024 to make the plan SHNE for 2024 with a 3% contribution. From 12/1/2024 until 12/31/2025, you can make the plan SHNE for 2024 with a 4% contribution.