To our conclusion, that TIME is the equivalent of Pastness, Presentness, and Futureness, combined, it may be objected, that the word Time is applicable to all the three cases; as we can say, past time, present time, and future time, all with equal propriety.
Source: wiktionary
What is posited as future is just the futureness of a sprout. That is, the sprout that will come is not future since when it exists, it exists at the present time.
Source: wiktionary
Furthermore, just as with the two passive syntheses, the third constitutive synthesis is a perspective of time giving us the elements of the futureness of the present and the futureness of the past.
Source: wiktionary