This seems quite similar to the Beis haLevi. We are discussing the cows which represent the years of abundance. He answers that Yoseif knew that Paroh's birthday was taking place in three days. Perhaps the default should be days and the exception is by Paroh's dreams. It is obvious that a seven DAY period of abundance is not logical.
Food production is guided by seasons of produce.
Likewise there is no famine for seven days, hence the units must be years. The gemara Rosh Hashonoh 10b says that Yoseif was released from jail on Rosh Hashonoh. If so, the dreams of the wine butler and baker also took place on Rosh Hashonoh, two years earlier. If so, Yoseif couldn't interpret their dreams to mean three years. Likewise Paroh's dreams which also took place on Rosh Hashonoh were fulfilled in the same year, as their fulfillment began during that year.