What are the relative merits of the different philosphies of time. Presentism states that only the present now exists, a la Julian Barbour. Eternalism posits an object spacetime stage where everything is already laid out simultaneously. The growing block universe states that only the present and past exists, but the future remains open, with the present flowing into the future, crystalizing it. Is timeless being or temporal becoming more fundamental?
Change, the flow of time, is obviously real. An objective universal "now", stretching across the universe, is obviously at odds with relativity. So I vote for "process eternalism": all times are equally real, and "coexist" (in some sense of the word "exist"), but they all exist in the mode of becoming, not in the mode of "timeless being".
The individual experience of time is not an experience of the whole of space at once, and not even an experience of a whole life at once: it is of a narrow individual state, that becomes another such state, that becomes another state, and so on until the end of life. Presumably this has to do with persistence-through-change in whatever part of the brain is the physical locus of consciousness. You are something, you came into existence, your existence is a series of changes in state, and eventually you will cease to exist.
For purposes of visualization and calculation, we can spatialize time, and think of your history as a "line" in space-time. We can even think of the histories of all the matter there ever was in space-time, as a "bundle" of such timelike lines. But we know from personal experience that the mode of being of our personal world-line is the mode of "becoming"; the world-line of a material object is made of the changes that happen to it ("made of time", one could say, though time itself is then "made of" change), and this applies to us too.
There are considerable difficulties in subsuming all the actual details of contemporary physical theory into this ontology. If we could canonically decompose the space-time history of the universe into a number of bounded "world-volumes" of narrow spatial width and finite duration, we could then say that each world-volume represents an elementary process, the persistence through time of a fundamental entity. For example, in a process-eternalist account of a cellular-automaton ontology, you could say that each cell has its own history and thus its own "local time". But it's hard to say what the "persistent fundamental entities" in the real world might be (D0-branes?).
By way of concluding, I would emphasize a few things. First, there is a limit to what physics can tell you about ontology and this is an example. Modern physics has been ontologically cut loose from phenomenological space and time; one is free to posit any sort of ontology, or no ontology at all, so long as you can start with empirical data, place it into the theoretical framework, and eventually get quantitative predictions which can be translated back into empirical consequences. This has given people the conceptual flexibility to dream up relativity and quantum mechanics, but it has also cut the ties between space and time as they are known in experience, and space and time as they are represented in mathematical physics. When physicists are asked to talk about the nature of time, they tend either 1) to use a fuzzy version of the intuitive concept of time, but with some alterations to acknowledge physics 2) to reify however they personally think about the mathematics, and say that space-time "is" an unmoving four-dimensional block, or (more rarely) that reality "is" an operator algebra, etc 3) say that reality is beyond time, or even beyond space and time, and that the nature of time is something for cognitive scientists and neuroscientists to figure out.
However, I think one must respect the subjective appearance of the world, if one wishes to do ontology. It is the one thing we do know to exist. For this discussion, this means that if we are going to talk about time, we have to respect the nature of time as revealed in experience, and that means the reality of change - of "becoming". Any ontology which denies that becoming is real, can be instantly falsified. Instead, one should use the reality of becoming (and the reality of the rest of phenomenology) as a clue to the nature of the reality that is described formally in our physical theories. Our experience is showing us part of the "true nature" of a very small part of the physical world (i.e. the little portion of brain in which consciousness resides). In the present instance, it is telling us that time is real. But as I remarked at the beginning, presentism (as well as the "growing block universe") is a problem from the perspective of relativity. Thus I opt for the peculiar compromise of process eternalism.
You left out relationism. In relationism, time is not independent of the configurations matter makes. Point of fact, time is none other than what clocks -- made up of matter -- read. It makes no sense to ask what if the clock reads out the wrong time from the 'actual' time because there is no actual time. If there are many many clocks, and nearly all of them agree except one, then it can be said that clock is synchronized wrongly. It makes no sense to ask what if all the clocks are synchronized wrongly if they all also happen to agree with each other.
The past in relationalism is none other than what the configurations of matter forming memories and records say the past is. if they all agree, that's what the past is. If most agree except one or two memories and records, those of them are suspect, and we go with the majority rule.
Time is not a container or a spatialized line where material events can be positioned into a timeline of history. That is a bad metaphor brought on to us by our language and brain structure. Time emerges from the configurations of matter itself.
Your question depends upon which interpretation of quantum mechanics you choose. The many worlds interpretation is compatible with both eternalism and presentism because all the branches are included. Interpretations with collapsing wave functions in real time tend to tie in with the growing universe interpretation, but not eternalism because how the wave function will collapse can only be determined probabilistically. Consciousness causing collapse interpretations tend to favor presentism at the time of consciousness.
Durationless instances do not exist. What we subjectively call now always has a temporal extent. It takes time to think, time to perceive, and time to act. This immediately rules out presentism. No clock has infinite resolution.
The flow of time is a nonexistent illusion with neurological underpinnings. When you process a spoken language sentence or listen to a melody, what happens is the auditory perceptions are cached into the phonological loop of working memory and stored in a linearized fashion. That is to say, not linearly in the brain, but when replayed in working memory, the contents of the phonological loop are played out sequentially in the same order in which they are first recorded. However, if you were to look into the brain, all you will see are the contents of the phonological loop all co-existing at the same instant. Ditto for visual motion as the brain also has a similar cache for visual motion and changes. The take home lesson is time all lies in your mind.
Time is not a measure of change because change can only be detected if the memory cache contains differing copies of the same object, or informational representations thereof, co-existing simultaneously. This is most readily apparent in visual change-blindness. A huge visual change is unnoticable if a brief flash is presented between changes. Once again, it is all in your mind.
Preverbal children live in a timeless world. It is only after learning language with its tenses and aspectual structure that they form a model of time in their minds. Roughly speaking, it looks like a timeline.
Causation lies in the mind. Certain kinds of correlations that are presented together to the brain under certain conditions are automatically assigned a causal cause-and-effect relation by the brain itself. Correlations between events exist, but causality only lies in the mind.