Andrew Huberman explains how different biological timing systems-from yearly and daily rhythms to 90-minute ultradian cycles-shape our perception of time, mood, energy, and performance. He describes how neuromodulators like dopamine, norepinephrine, and serotonin alter how fast or slow time feels in the moment and how we remember events later. He then connects these mechanisms to trauma, novelty, and habits, showing how deliberate routines and environmental variation can structure our days, influence memory, and support better focus.