Our everyday ideas about the progression of mental time are wrong: they leave no room for the fact that every agent has a different causal history. To be sure, those different pasts are intermixed over longer spans of time, and every agent is eventually influenced by what has happened in the common, remote history of its society. But that's not what one means by now. The problem is with the connections between the moment-to-moment activities of largely separate agencies.
When a pin drops, you might say, I just heard a pin drop. But no one says, I hear a pin dropping. Our speaking agencies know from experience that the physical episode of pin dropping will be over before you can even start to speak. But you would say, I am in love, rather than I was just in love, because your speaking agencies know that the agencies involved with personal attachments work at a slower pace, with states that may persist for months or years. And, in between, when someone asks, What sorts of feelings have you now? we often find our half-formed answers wrong before they can be expressed, as other feelings intervene. What seems only a moment to one agency may seem like an era to another.
Our memories are only indirectly linked to physical time. We have no absolute sense of when a memorable event actually happened. At best, we can only know some temporal relations between it and certain other events. You might be able to recall that X and Y occurred on different days but be unable to determine which of those days came earlier. And many memories seem not to be linked to intervals of time at all — like knowing that four comes after three, or that I am myself.
The slower an agency operates — that is, the longer the intervals between each change of state — the more external signals can arrive inside those intervals. Does this mean that the outside world will appear to move faster to a slow agency than to a faster agency? Does life seem swift to tortoises, but tedious to hummingbirds?