Time is indeed relative.
I was talking to Noah about this this morning — why one feels the time in the morning always flies by? Theoretically time is uniform, it ticks by the second all the time, at the same pace. It doesn't change over the course of a day, so why morning time feels short? Well, we are not talking about bad days that you felt like indefinite long, but just a regular Wednesday morning.
So here is my theory: I think time feels different because your brain is operating at a different speed → in the morning, your brain is slow to boot up, thus the constant flow of time feels a speed train passing you by, again, this is arguably the perception of time by your brain (exactly). On the flip side, time will then feel short when your brain is working at a higher speed. The experience will be when you are in the zone of writing code or doing something, that you forgot about time and felt it was really short! I'm sure everybody will echo this experience. Following this logic, the feeling of time should be defined as an efficiency factor, or density, or velocity,, of experience, that within a fixed number of ticks, the more your brain worked and perceived, the higher the density, that the shorter the time feels. Interesting. I wonder whether this is what relativity theory says?
So, what is really time? Is it just another aspect of perception like I have just said. We know it is a complete artificial thing, because there isn't such a thing called TIME in nature. I like the motto of Movado swatches that there isn't really 24 hours a day, just a fact that sun rises and sets everyday, which then defines the notion of time. Therefore there is a single dot on its watch's face that represents, sun? and the minute and hour arms just go by it that simulates sun rise and sun set. How genuine!
Time, thus, is really a human invention, and quite an arbitrary one, that we divide time into 24 hours a day. Actually this hasn't been always the case either. We know at different time and by society people had used different calendar; so many have used different ways to describe time — how about bars on a prison wall, or a marks on a tree bark! They are all indication of elapse of, time! 24-hour day is just one of many ways human have used, and happens to be the going standard when I'm writing this. The problem at its core is a math one ← earth doesn't go around sun in a nicely rounded integer value (well, integer is another human invention to describe nature, so it seems human is caught by his own inventions) So regardless how we are wishing to give it a good chunk, say 24, or 16, or 17.5 even, there is always a bit of residual to count in order to make it accurate — accurate in the sense that what human makes of it matches what nature shows (think of solar year, aka. tropical year, that has 365.24219 days, or, be precise, ephemeris days). So you, every single noun in such statement is essentially another human invention that is to describe a, thing, which requires definition, and if only all the definitions are hold true at the same time, will such a statement be true and meaningful (well, even the word "meaningful" or "true" requires definition and scrutiny! How convoluted human language has become!!!!!) In the book Seventy Great Inventions of the Ancient World, it talks quite a bit of examples of time, such as the Maya Calendar. So if you are not yet convinced that time is subjective, read it.
I can't find who said this, that the root of human tragedy is that the wise takes every step full of hesitation, while the fool take every resolutely (智慧的人每一步都犹豫不决，愚蠢的人每一步都步伐坚定).
— by Feng Xia