In SharePoint Calendar lists, fields [Start Time] and [End Time] do not exist at the Site Column level.

I'm doing SP app development and have the following problem.

I need to check Start time and End Time in SharePoint Calendar using CAML query and then add a new event to Calendar list using the Start time and End Time that user has entered in 2 datapickers in the form.

function AddCalendarListItems() {
        // DateTime start = Convert.ToDateTime(_properties.AfterProperties["datepicker"].ToString());
        var SD = document.getElementById("datepicker").value;
        var SThh = document.getElementById("St1").value;
        var STmm = document.getElementById("St2").value;
        var ED = document.getElementById("datepicker2").value;
        var EThh = document.getElementById("Et1").value;
        var ETmm = document.getElementById("Et2").value;
        var T = document.getElementById("Title").value;
        var S1 = SThh;
        SD = SD.slice(6, 10) + "-" + SD.slice(0, 2) + "-" + SD.slice(3, 5) + "T" + SThh + STmm + ":00Z";
        ED = ED.slice(6, 10) + "-" + ED.slice(0, 2) + "-" + ED.slice(3, 5) + "T" + EThh + ETmm + ":00Z";
        alert("SD= " + SD + " ,  ED= " + ED);
        var siteUrl = SiteCollurl + "/SharePointApp11";
        var clientContext = new SP.ClientContext(siteUrl);
        var oList = clientContext.get_web().get_lists().getByTitle('BookingRoomManager');
        var ListItemCInfo = new SP.ListItemCreationInformation();
        var newEvent = oList.addItem(ListItemCInfo);
        newEvent.set_item("Title", T);
        //var sss = Date.now();
        //alert("Todat:  " + sss);
        newEvent.set_item("Start Date", SD);
        newEvent.set_item("End Date", ED);
        newEvent.update();
        clientContext.executeQueryAsync(Function.createDelegate(this, this.onQueryAddCalendarSucceeded2), Function.createDelegate(this, this.onQueryAddCalendarFailed2));
    }

    function onQueryAddCalendarSucceeded2(sender, args) {
        alert("Success");

    }

    function onQueryAddCalendarFailed2(sender, args) {
        alert('Add new item to the calendar failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }​

But I receive the following error:

Add new item to the Calendar failed. Column 'Start time' does not exist. It may have been deleted by another user.

I've checked and 'Start time' does exist. So it seems in SharePoint Calendar lists, field [Start Time] and [End Time]  exist but do not exist at the Site Column level.

Please advise.