Please refer to the below code for your reference.

odoo.define('planning_gantt.PlanningGanttView', function (require) {
'use strict';

const PlanningGanttRenderer = require('planning.PlanningGanttRenderer');
const fieldUtils = require('web.field_utils');
const { patch } = require('web.utils');
const utils = require('web.utils');

patch(PlanningGanttRenderer.prototype, 'PlanningGanttLabels', {
_generatePillLabels: function (pills, scale) {
const dateFormat = moment.localeData().longDateFormat('l');
const yearlessDateFormat = dateFormat.replace(/Y/gi, '').replace(/(\W)\1+/g, '$1').replace(/^\W|\W$/, '');
pills.filter(pill => !pill.consolidated).forEach(pill => {
const localStartDateTime = (pill.start_datetime || pill.startDate).clone().local();
const localEndDateTime = (pill.end_datetime || pill.stopDate).clone().local();
const spanAccrossDays = localStartDateTime.clone().startOf('day')
.diff(localEndDateTime.clone().startOf('day'), 'days') != 0;
const spanAccrossWeeks = localStartDateTime.clone().startOf('week')
.diff(localEndDateTime.clone().startOf('week'), 'weeks') != 0;
const spanAccrossMonths = localStartDateTime.clone().startOf('month')
.diff(localEndDateTime.clone().startOf('month'), 'months') != 0;
const labelElements = [];
if (scale === 'year' && !spanAccrossDays) {
labelElements.push(localStartDateTime.format(yearlessDateFormat));
} else if (
(scale === 'day' && spanAccrossDays) ||
(scale === 'week' && spanAccrossWeeks) ||
(scale === 'month' && spanAccrossMonths) ||
(scale === 'year' && spanAccrossDays)
) {
labelElements.push(localStartDateTime.format(yearlessDateFormat));
labelElements.push(localEndDateTime.format(yearlessDateFormat));
}
if (!spanAccrossDays && ['week', 'month'].includes(scale)) {
labelElements.push(
localStartDateTime.format('LT'),
localEndDateTime.format('LT') + ' (' + fieldUtils.format.float_time(pill.allocated_hours, {}, {noLeadingZeroHour: true}).replace(/(:00|:)/g, 'h') + ')'
); }
if (scale !== 'month' || spanAccrossDays) {
labelElements.length = 0;
labelElements.push(pill.display_name);
}
pill.label = labelElements.filter(el => !!el).join(' - ');
}); } }); });