The first point in time is acquisition of a qualifying nisab; from that point early payment is permitted before the year ends. The second point is completion of the year when the obligation ordinarily falls due.
Therefore advance zakat cannot be equated with a payment made before nisab ownership. How a prepayment is reconciled with the year-end assessment is a separate technical question.
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Miscellaneous Zakat Rules: Substitutes, Value, Grazing and the Zakat Year
The first point in time is acquisition of a qualifying nisab; from that point early payment is permitted before the year ends. The second point is completion of the year when the obligation ordinarily falls due.
Therefore advance zakat cannot be equated with a payment made before nisab ownership. How a prepayment is reconciled with the year-end assessment is a separate technical question.