This text proposes that time is essentially related to one's visual metabolic rate. Metabolic rate is regulated by the speed of the intake of energy, the rate of the Production of adenosine triphosphate (ATP) to the visual areas. The author's working hypothesis is that the visual area of the brain known as human V5, the region involved in motion detection, may be the region most responsible for time perception. Our time sense from all the senses is, thus, compiled in the visual region, the speed of the human perception of reality. Time is the relationship of the human perception of reality and the rate that the reality itself is taking place (given by light waves in the environment). Hence, vision (and the visual cortex area V5) may be the vitally important aspects in answering the question: what is time? When we are not looking at a clock, time may be governed by our rate of metabolism; rate of the production of ATP by the mitochondria in V5. For example, when general human metabolism (and V5) is fast, time runs slow. When metabolic rate is relatively slow, time runs relatively faster. Many factors enter into the speed of metabolism such as age, sex, drug effects, velocity compared to speed c, states of boredom or excitement, darkness or light and mental states such as sleep. The relationship between time and space is discussed with the metabolic rate of V5 in mind. Because the uncertainty principle and the quantum picture of reality are adopted, this model qualitatively quantizes space and time, showing why they must forever be connected i.e. space-time. This idea is discussed in relation to Zeno's paradox, which suggests that space and time are indeed quantized Events, instants and entropy are defined Reality can be understood in terms of the speed of the processing of instants. The arrow of time is pictured as caused by long-term potentiation of synaptic neurons within the brain. Minkowski-Einstein space-time is analyzed and compared with the visual metabolic rate. The probable consequences of this model are proposed.