I think you're onto something, but I don't think it has to do with plasticity, but novelty.

Consider the brain as a giant recording device with very good compression based recognizing patterns from previous data. So the first time you eat an apple, it stores a lot of data because it's a new experience. The next time, it stores something more like "like the last apple, but a little more tart".

I think our perception of time (at the macro scale) is roughly a perception of how much new data our compression-oriented brain is storing. It's the sensation of accumulated novelty.