How long a clip runs

Three behaviors: follow the movement, a fixed length, or at least a fixed length.

As long as movement lasts — the clip matches the event, closing once the scene has been quiet for the set period. Brief movement makes a brief clip. Most economical with disk space.
A fixed length — every clip is the same length whatever happens. Predictable file sizes, but a long event becomes several clips, and a two-second event still costs a full-length file.
Fixed length, or longer if movement continues — guarantees you always get at least the set length, and doesn't cut off an event that's still going. This is the default, and usually the one you want.

Only the settings a mode actually uses are shown, so there's never a slider on screen that does nothing.

In the two modes that can run long, the maximum is a hard ceiling so a very busy afternoon can't produce one enormous file. When a clip is cut short by it, the sidecar records that — otherwise you'd have no way to tell a truncated clip from an event that genuinely ended.

The cooldown is a different thing entirely: it's the minimum gap between separate events, and it's what stops one long incident becoming a pile of clips.