The keyword term is a noun phrase. It functions as a single grammatical unit to name a specific, calculable point in time. The core of the phrase is the noun "days," which is modified by the preceding number and the subsequent prepositional phrase to create a singular temporal concept.
Grammatically, the phrase is constructed around the head noun "days," which is pre-modified by the determiner and quantifier "45." The noun is then post-modified by the prepositional phrase "before September 11, 2025." This entire construction allows the phrase to act as the subject of a sentence (e.g., "[The date] is a critical deadline"), the object of a verb (e.g., "We will analyze [the date]"), or as an adverbial phrase of time that modifies a verb (e.g., "The event occurred [on that date]").
In practical application, identifying the phrase as a noun phrase is crucial because it allows it to be treated as the central topic or entity of discussion. The specific date designated by the phrase is July 28, 2025. This is determined by counting back 45 days from September 11: subtracting 11 days in September leaves 34; subtracting the 31 days of August leaves 3; subtracting 3 days from the 31 in July arrives at July 28.
