It would be more correct to say, the speed of time defines what space is. Space is the set of relations, defining the fastest possible signals, between points, or assemblies of values of fundamental constants, that we call particles.
Subjective timespeed certainly varies subjectively. Young people typically experience time moving much more slowly; a single years difference in age feels like a gulf, but as we age a year viewed as a percentage of lifespan, recedes. As we grow familar with experiences, we automate responses, to use fewer resources, and focus energy on novelty. As we age, we risk writing off more of our experiences as, not deserving our full attention, and it flying by.
It's interesting to compare boredom, and meditation. I think we can understand boredom as being more intensely painful for the young, because they are feeling driven to test themselves, to develop their faculties and skills. But when we have done so, it is skillful to develop beyond boredom, so we can sit with problems for longer and more deeply, without rushing to conclusions; and curb our compuliveness and immediate reactiveness.
Kahneman in 'Thinking Fast and Slow' prrovides a neurological basis for this. Our intuitive responses are tuned to be 'good enough', and our slow analytical resource-intensive responses are typically triggered when those automatised standard heuristics fail in prediction. Our brain's 'clock speed' ramps up, spending more mental energy and subjective time processing each input.
The research on DMT is very interesting. It's thought to be endogenous, and associated with being born, and near-death experiences. The theory goes that it opens the brain in a radical way bith to inputs from the moment, and to 'wild' free-association with any memories or inferences. While being born, there is no subjective memory-bank to draw on, but there is no more critical time to going on to develop. And DMT is implicated in 'your life flashing before your eyes' near death experiences, as literally a rapid scan using all your brain's resources for anything relevant or useful. In medical trials patients describe epic, life-changing elaborate visions, as happening in as little as five minutes of apparent unconsciousness.
Biologically, it was thought experiencing time passing would be some kind of higher-level emergent function. But it has turned out every cell has a sense of day and night, these synch up towards indicating time passing. When people go under medical anaesthesia or go into a coma, very often the sense of time passing is lost, in a way it isn't during sleep or other kinds of unconsciousness.
We have an idea that time passing is a 'universal clock', so that we can relate events systematically between everywhere. But we can't, because all the 'points' are just moments when the matter-waves of uncertainty are interupted by taking a measurement. A lot of information is fundamentally 'folded-in' to quantum encertainties, 'inside' the uncertainty-principle, in a way that involves time certainty disturbing position certainty and vice versa. The systematic relation of time is limited to classical Relativistic picture. Using Noether's Theorem, we can understand space-time not as an inert background specifying relations between 'pixels', but as sets of locality relations defined by symmetries under transformation, and that what we call dimensions are that and are directly equivalent to conservation laws. The degree of uncertainty of a quantum object relates to how many states it can be in, and we an relate that to conservation of information - the 2nd law of thermodynamics tells us that the forward direction in time always involves maintaining or increasing the possible sub-states. Spacially, the Feynman diagrams of interactions can be rotated and be equivalent. But the Arrow of Time emerges because it is equivalent to a symmetry property, transformation into the same or more sub-states of quantum objects
(Chiribella's Purification Principle tells us this conservation of information/entropy increase relates to the spreading out but not concentrating of correlations, with quantum behaviour as defined by states small enough the spreading out rule doesn't dominate, and new pure states can emerge from signal-seperated and therefore quantum objects).