A horizontal timeline charts patient flow through stages like Waiting, Vital, and Doctor, with colored bars and labels showing durations. The chart uses a custom `d3.timeline` function built with D3 v3, rendering SVG elements. It stacks rows, applies a 15-minute time axis with `d3.time.format`, and supports custom tick formatting and interactive navigation. Colors are mapped to each stage, and the example demonstrates how to configure margins, stacking, and axis labels for a clear temporal sequence.