Each hotspot is a pixel a satellite radiometer found to be burning as it flew over. Once ground has been detected burning it stays on the map as scar. The bright marks are hotspots seen within the previous five hours, coloured by heat output and recency.
The satellites do not watch continuously. They pass overhead roughly six times a day, so only — of the — hours here contain a real observation. The ticks under the timeline mark those hours. In between, the map holds its last known state — it does not interpolate a moving fire front, and a run that happened between two passes appears all at once on the later one.