I don't really see this as debatable. The quarterly is clearly late because the credit balance didn't exist on 7/15. There is no grace period for interest penalties, only for notice requirements.
I agree with the other responses and see this is pretty clear. If you shop is split, I would argue you all haven't read the notice.
QUOTE
Q/A-12 Notice 89-52
Q-12: May an employer treat all or a portion of a credit balance in a plan's FSA as a payment of a quarterly installment?
A-12: An employer may treat all or a portion of a credit balance in a plan's FSA as a payment of a quarterly installment.
Example 5 --Assume the same facts as Example 3, except that an amount in excess of the 1988 minimum funding requirement was contributed during 1988 and that such contribution resulted in a credit balance of $10,000 on December 31, 1988. It was determined in Example 3 that the amount of the first quarterly installment due on April 15, 1989 is $6,250. At that time, the credit balance, with three and a half months' interest, equals $10,227. Even if no contribution is made by April 15, 1989, the first installment requirement is satisfied because the credit balance with interest exceeds the amount of the quarterly installment due. The amount of excess, $3,977, with three months' interest to the due date of the second installment, is $4,054 and may be used to reduce the amount required to be contributed for the second installment. Therefore, as long as $2,196 [$6,250 - $4,054] is contributed by July 15, 1989, the second installment requirement will be satisfied. The full $6,250 must be contributed for the third and fourth installments unless additional contributions are made for the 1988 plan year on or before September 15, 1989.
Contributions for the prior plan year will not be reflected in the determination of any credit balance until they are actually contributed to the plan. The intent to contribute the required amount within 81/2 months after the end of the prior plan year is not sufficient. For example, in the previous example, if no contribution for the 1988 plan year had been made by April 15, 1989, no credit balance could have been taken into account in determining the amount needed to satisfy the first installment requirement, unless the amount of credit balance as of December 31, 1987 was greater than the 1988 minimum required contribution.