Defined modally, possibility is what exists at one time and not at another, making time a backdrop or domain of the possible. This is incoherent for all sorts of reasons: it makes time static and overly space-like; it leads to contradictory notions of different times existing at the same time; and it makes the accident of when something exists into a substance.
So why not flip the order of existence: possible existents are the backdrop of time. Time is thus an abstraction from the concrete fact that (unactualized) possibilities are incompatible both with other possibilities and with their actualities. Briefly, time arises from the way in which possibilities fall under the principle of contradiction.