The endTime property of the TextTrackCue interface returns and sets the end time of the cue.
A number representing the end time, in seconds.
In the following example a new VTTCue (which inherits from TextTrackCue) is created starting at 0.1 second and ending at 0.9 seconds. The endTime property is then printed to the console.
let video = document.querySelector("video");
let track = video.addTextTrack("captions", "Captions", "en");
track.mode = "showing";
let cue = new VTTCue(0.1, 0.9, "Hildy!");
console.log(cue.endTime); // 0.9
track.addCue(cue);