Updating minTime and maxTime Dynamically not working

[MihirChichria]

$.ajax(
    {
        type: 'POST',
        url: "/admin/calendar-helper.php",
        data: {
            getTimeSlots: true,
            date: selectedDate
        },
        success: function (res){
            let data = JSON.parse(res);
            // console.log(data.start_time);
            // console.log(data.end_time);
            $("#calendar").fullCalendar('option', 'minTime', data.start_time);
            $("#calendar").fullCalendar('option', 'maxTime', data.end_time);
            $("#calendar").fullCalendar('render');
        }
    });

$("#calendar").fullCalendar('render'); not rendering