The startTime property of the TextTrackCue interface returns and sets the start time of the cue.

A number representing the start 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 startTime property is then printed to the console.

let video = document.querySelector("video");
let track = video.addTextTrack("captions", "Captions", "en");
track.mode = "showing";

let cue1 = new VTTCue(0.1, 0.9, "Hildy!");
console.log(cue1.startTime); // 0.1
track.addCue(cue1);