different eligibilty for EE groups in Safe harbor

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Can an employer have different eligibility provisions for different groups of EE's in a safe harbor 401(k) (assuming they pass coverage)?

For example: one plan, two employee groups. Group A is eligible to contribute and receive standard safe harbor match after 3 months of employment and age 21. Group B is eligible for the exact same contribution rate and match but not until after completing 6 months of employment and age 21.

If the two groups pass coverage, is this permissible?