Pass Date Values from Ajax Call to MVC

MY Ajax call

 $('#QuickReserve').click(function () {
        var now = new Date();
        alert(now);

        var _data = {
            'ComputerName': _computerName,
            '_mStart': now.toTimeString(),
            '_mEnd': now.toDateString()
        };
        $.ajax({
            cache: false,
//            contentType: "application/json; charset=utf-8",
            type: "POST",
            async: false,
            url: "/Home/SetMeeting",
            dataType: "json",
            data: _data,
            success: "",
            error: function (xhr) {
                alert("Error");
                alert(xhr.responseText);
            }
        });
    });

MY C# code

 public ActionResult SetMeeting(string ComputerName, DateTime? _mStart, DateTime? _mEnd)
        {
           }

DateTime values are not received at code end..... They just appear blank. In jquery when i tried to

'_mStart': now.toTimeString(),
            '_mEnd': now.toDateString()

to datestring does return today's date, but, i want time part of date time also.