Parashas Behar · Aliyah 2 · Passuk 25:15
Chabad.org — English translation + Rashi
Torah Temimah cites Arakhin 29b.
English: “According to the number of years of crops.” Even if there are three harvests in two years, he may not redeem for less than two years.
Classical derasha (Bavli Arakhin).
The two-year minimum for redemption is measured in years, not in the number of harvests that may occur within those years.