JSFiddle - React, Tailwind, and code Playground

HTML

<input type="date" id="jour-debut" value="2023-11-16">
<input type="time" id="heure-debut" value="10:30">
<input type="time" id="heure-fin">
<button id="add-minutes">Add 15 minutes</button>

JavaScript

const jourDebut = document.getElementById('jour-debut');
const heureDebut = document.getElementById('heure-debut');
const heureFin = document.getElementById('heure-fin');

let dateDebut = new Date(jourDebut.value + " " + heureDebut.value);
let dateFin = new Date(dateDebut.getTime() + 15 * 60000);

heureFin.value = ('0' + dateFin.getHours()).slice(-2) + ':' + ('0' + dateFin.getMinutes()).slice(-2);
// heureFin.valueAsDate = dateFin;

document.getElementById('add-minutes').addEventListener('click', (e) => {
  dateFin = new Date(dateFin.getTime() + 15 * 60000);
	heureFin.value = ('0' + dateFin.getHours()).slice(-2) + ':' + ('0' + dateFin.getMinutes()).slice(-2);
  // heureFin.valueAsDate = dateFin;
});