Time is a concept that pervades our thinking so much that it confuses even our thinking about time. Here are just a couple of examples.
The first is a thing from science fiction, or at least Calvin and Hobbes. This is where time travel takes time. It seems natural: you go in the time machine, then the time machine travels in time, and that takes some time. As in you spend some time travelling in time. You sit in the time machine for half a minute, say.
Now, how does that make sense? There’s time that’s outside of time? We imagine time at the background of all events and happening and thus we imagine even time travelling taking time. But time travelling means skipping past some amount of time. Thus, you can’t just assume time would be passing “while” you’re doing it.
I don’t know how time travel would really be experienced, but if there was “time” spent doing it, that would imply something we don’t know about and that seems really weird, some kind of meta-time.
Meta-time is also involved when we imagine time being somehow stopped. That’s another meaningless idea. Stopping something can only meaningfully mean stopping its progress in relation to the progress of time. If you were to stop time, how would you determine how long it’s stopped? For five minutes, say? But those five minutes would not pass because time was stopped. Again, there would have to be some flow of time besides the flow of time.
A third place where the implicit idea of meta-time is involved is when we think about time somehow flowing ahead.
Is the present a moving point so that only the present exists, or do all points in time exist the same way? That question is nonsensical. Only the present exists at the present (the same way only things that are in particular part of space are in that part of space), but the question of whether other times exist can’t be formulated sensibly. Does the past still exist, or the future yet exist? Well, no, because what is in the past is in the past, not now or “still”, and what is in the future the future only. The past and the future themselves are parts of time, not something that exists the same way as their contents. At the same time, though, it’s not meaningful to say that the past and the future do not exist, as in either do not exist now or do not exist because they do not exist now. Saying that implies they could somehow exist now, that even if it is impossible that statement is somehow meaningful — that there is something that people who say so mean that you can object to.
It’s no mere apparent problem that when you say something in the future exists or doesn’t exist now, you attach both “now” and “in the future” to the same thing. It’s a real problem in terms of meaning, because there just isn’t anything that that could mean. This is similar to the paradox where the future supposedly becomes determined just because it is “now” true that something will have happened a certain way in the future. What do you mean “now true that in the future”? The statement uttered now may be true (or untrue), but it’s a statement about the future; the fact that it refers to has no “now” component. You could also say that it’s true timelessly, so not “now”, but that’s just because the statement itself contains the mention of the time so you don’t need to further specify when it’s true. When it really is true is at the time specified, and the talk about timelessness is not exactly incorrect but in any case needless.
Back to time flowing: this assumes meta-time because flowing is movement. When we say all times exist or don’t as if it makes a difference, we need to covertly assume something equivalent with meta-time to which we relate the statement: at this moment in meta-time when time has flowed this far, the other times still exist, or don’t, on different parts of the timeline, all of which exists at once. After all, how else can we have to determiners of time, as in “the future exists (and not only will exist)”? There must be a second level of time, even if it’s not quite in the same sense as in the time travelling and time stopping examples. Assuming only one system of time, there’s nothing that the one defending the notion of times besides the present existing can meaningfully say that the opponent can disagree with without already assuming something like this. Different times, or rather their contents, exist at that time and don’t exist at others. Just about everyone should agree about that in some sense, and that’s the only meaningful sense. Therefore, most of the arguments about the matter are probably about nonsense.
In conclusion: we get impossible results when thinking about time because we naturally assume time in the background. This is just one example of how we are unable to analyse things properly when we also use the unanalysed concept at the same time. When we think about our natural basic concepts, we have to stop assuming them at the same time. This is difficult even for philosophers.