8.5 months after a mid month date..plan termination

If a plan is terminated mid year, the 430 regs tell us to use the termination date as the val date and treat the plan for 430 purposes as having a short plan year. The minimum is due 8.5 months after the end of the short plan year. Do we count 8.5 months from the end of the month like with the final 5500 filing or is a more precise counting required. For example, if the plan terminated today 10/23/2023 is the contribution due date 7/15/2024 or some other date?

Forgetting about the short plan year and termination for the moment, what if the PYE and valuation date was 12/1 instead of 12/31. Would your MRC due date still be 9/15 or 8/15 (8/16)? I think it's the August date. So in your situation I think it's due 7/7ish. Also, why risk a late contribution for 8 days over an interpretation question/gray area?