Look at pages 70 & 71 (document, not pdf) of the BSA/AML Examination Manual. The summary statement you will find there is:
The phrase “initial detection” should not be interpreted as meaning the moment a transaction is highlighted for review.
In your scenario, your position would have to be that your investigation began on the date you DID identify the transactions. To paraphrase and condense what you will read in the Manual, you begin the countdown to the required filing date when it becomes apparent to your bank that a SAR filing is necessary.
The Manual, supported by prior interpretations, reflects more common sense than the regulation; they do not want "hip-shot" filing decisions.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.