Startup Safe Harbor Non-elective 401(k)

I have a last-minute startup 401(k), calendar year, going with 3% non-elective as the safe harbor with discretionary profit sharing.

Prior to the SECURE Act we would make the plan effective 1/1/2020 for the profit sharing portion of the plan, and the deferral and safe harbor portions effective October 1 allowing for implementation time and the safe harbor notice.

Now that the SECURE Act no longer requires a safe harbor notice (although for now we are going to continue to provide safe harbor notices for non-elective plans), and the nonelective can be added after the fact, is there any reason the safe harbor cannot also be effective January 1, 2020, or does the safe harbor still need to be effective on or after the date the deferrals are effective for the first year?

Or let's say they want to wait on the safe harbor until the year is over and are ok with the 4%.  The deferrals still need to start 10/1/2020 so we have a 3 month initial plan year for the deferrals, but what date would we make the safe harbor effective in this case?  The nonelective must apply to all of 2020, correct, so wouldn't the effective date need to be 1/1/2020?

Or possibly I'm overthinking this because the recordkeeper needs the plan design yesterday to set up for Oct 1.

Thanks for your help.

I think I am overthinking.  You can't really have safe harbor without elective deferrals, so I'm thinking 10/1/2020 would need to be the start date for the safe harbor too.