The unity of time in Heidegger

I was in a class a year ago or so that presented the unity of time in Heidegger as the directionality of time, the way it only "flows" one way. This, I realize now, was a good way to explain easily to a class that was quickly getting almost unretreivably lost in the second division of Being and Time what Heidegger was generally getting at. But now I see it is a bit too Kantian a way of conceiving it: the professor was looking for something that would be structurally a priori about the phenomenon itself such that it could be unitary (as Heidegger puts it mockingly, this something would be "a network of forms which a worldness subject has laid over some kind of material" 417). Heidegger insists, however, that the temporality he is talking about is not unified because of some a priori condition that is inherent to time, but is a product of the intertwining of Being and time--that is, it is time's consitution and determination of Being that gives time a unity.
When I speak of a "unity" of time, like Heidegger I am talking about what guarantees the togetherness, or "equiprimordiality" as Heidegger likes to put it, of the three "ecstases" of time, the future, the present, and the past. Time is a structural unity of these three terms, and something about time guarantees that these terms unify. Now, if the "uni-directionality" of time--its ability to only move meaningfully forward--isn't it, what could it be?
Heidegger says that it is the finiteness of time that guarantees its unity. Talking about the world and time's relationship to it, he outlines what this means:

The existential-temporal condition for the possibility of the world lies in the fact that temporality, as an ecstatical unity, has something like a horizon. Ecstaces are not simply raptures [or ways of existing temporally] in which one gets carried away. Rather, there belongs to each ecstasis a "whither" to which one is carried away.
-Being and Time, II, 4, ¶69c, p. 416.

Now, Heidegger is talking about the unity of the phenomenon of the world, but it clarifies a little about the unity of the So time opens itself up into a world--i.e. makes a world possible--because of its finiteness to some degree. Let's elaborate.
What Heidegger is getting at here is how a world opens up for us because of time. That is, he is getting at how time unfolds itself into a world, onto a place where we consitute our significance. This world is us, and is not us at the same time: it is us in the sense that we are in that place where we constitute our significance; it is not us in the sense that our significance can either be larger or smaller than us ourselves. As Heidegger puts it, "Dasein is its world existingly" (416). What this means is that so long as I exist, I have a world where I disclose or constitute my significance. Heidegger calls this place the "there" of disclosure. That is, whenever I understand myself and thus exist as myself, I disclose that significance that I inhabit and yet do not inhabit. I disclose it as a "there." The "there" that is disclosed, then, is really that significance that is me and is not me. This "there" then is the world. Now, in this passage, he is simply getting at how time allows that "there" to be, how it unfolds itself in its existing as and with us as the world.
Heidegger says that to each ecstasis belongs a "whither" because temporality has "something like a horizon." Now, what this means is that because time is finite to some degree--i.e. to the degree that it is not actually its finiteness qua finite, but is somewhat asserting its finiteness in being a "horizon" for something--because time is finite to some degree there can be a "there," i.e. time can unfold itself in disclosure. What do we mean by this? When there is disclosure, i.e when Dasein understands itself and thus inhabits and constitutes its significance, there is a world. This emphasis on "when" and "there" in this sentence means that the "there" is constituted by the "when" and particularly how the "when" (i.e. Time) is structured. This is what we mean. The structure of the "when," the structure of time, Heidegger says, is finite. If time is finite, it is not a series of discreet events or moments that, like a timeline, follow one another on and on into eternity and "in which" things occur. Rather, it exists precisely as a "there," as a disclosure. What we mean by this is that time exists so long as Dasein exists: time is essentially what determines me and is my “there” so long as I am, but which no longer exists without me. It should be clear that time is tied up with Being, then: if I no longer exist time is no longer existent either. But the crucial thing is that time determines my existence in every other case--i.e. in every other case than my non-existence, my non-Being. Time, then, as a “there” that I exist alongside so long as I am is a way of being in which I exist always. But unlike other ways of being, it is the one that supercedes or transcends all of them: it determines every other way that I can be. This is because it is the structure of those ways of being--not in the sense that it is the "essence" underlying all particular moments in which I exist temporally, but rather in the sense that in a way of being that is a way of being, time will get constituted in the way in which that way of being exists. This structure is “there” disclosed according to the ecstasies. Thus the world, which is the significance that gets constituted in the “there,” is always also (and primarily) constituted by time because of time's finiteness in this particular way. The "there" will always be temporal.
This all outlined, we can see that all this is only possible based on the essence of time as finitude, as determinate. The "whither" that belongs to each ecstasies and constitutes the “there” whenever it is conditioned by a definite “when.” That is, disclosure occurs in a definite way; one exists definitely or determinately: this is all due to the fact that there is a definite type of “when.” This is also due to the fact that this “when” has definiteness in the way we just described—not as a definite “point in time,” but in a definite way of being. Let’s elaborate. Because time is determinate, each of the ecstases has a determinateness in the sense that it has a way of being that it conditions specifically and which corresponds with it: this is what Heidegger means when he says “ecstaces are not simply raptures in which one gets carried away.” The past is not simply this area of time behind us filled up with various points, the future is not this indefinite area ahead of us. Each is a way of being, because time unifies the ecstases in its finiteness, in its lending finiteness to the area of the past, the future, and the present. What does the past, future, and the present look like then? Well, quite simply, as ways significance come to constitute a way of being. In other words, time in its unity—in its finiteness—comes to look like a specific way that significance comes gets dealt with by Dasein. If one is existing futurally, Heidegger says that significance will be dealt with in such a way that the world and Dasein itself will seem like beings that are “for-the-sake-of” Dasein. This is contrasted to the present, in which the world and Dasein will be dealt with as beings that are “in-order-to;” as things that are there “in-order-to” help or hinder Dasein in some way of its being. The past is dealt with as that “to which” Dasein is “abandoned.” Now, each of these ways of being is essentially what it is because it is temporal, and each is definite and is dealt with as a mode of significance because time is finite. Because time is not a set of points, but disperses itself as definite ways that Dasein can exist, and unifies these ways in its finiteness—because of this, time can be seen as unified, and not because of the particular “direction” it “flows.” If there is a directionality of time that bears on every mode of being, this would have to be because time unifies itself in finiteness: that is, because it exists as a way for Dasein and beings more generally to be.