C# Interacting with Database In async way, not working.

I just wanted to create a dummy ASP.NET MVC project where i wanted to explore more about async & await.I created async methods in DB access Layer and Repository Layer and i also make sure that the action is also written in async way. I noticed that a single method takes around 7ms to execute, so logically if i call the method 3 times i also should take 7 ms or around 7ms ! But its taking about 20-23 ms. I am sure that i am doing something terribly wrong. My Code snippet goes below:

DATA ACCESS LAYER:

    public async Task<DataTable> DtGetAllCustomers()
    {
        await Task.Run(() =>
        {
            _dtCustomer = new DataTable();
            _connectionString = Repo.GetConnString();
            _spName = "spGetCus";
            _spParameters = new SqlParameter[]
            {
            new SqlParameter("@QryOption",1)
            };
            using (var conn = new SqlConnection(_connectionString))
            {
                using (var cmd = new SqlCommand())
                {
                    cmd.Connection = conn;
                    cmd.CommandText = _spName;
                    cmd.Parameters.AddRange(_spParameters);
                    cmd.CommandType = CommandType.StoredProcedure;
                    conn.Open();

                    using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                    {
                        da.Fill(_dtCustomer);
                        conn.Close();
                        da.Dispose();
                    }
                }
            }

        });

        return _dtCustomer;
    }

REPOSITORY:

 public async Task<List<CustomerModel>> GetAllCustomers()
            {
                _dtCustomer = await _customerDal.DtGetAllCustomers();
                List<CustomerModel> allCustomers = new List<CustomerModel>();
                return allCustomers = (from DataRow row in _dtCustomer.Rows
                                       select new CustomerModel
                                       {
                                           CustomerId = (int)row["CustomerId"],
                                           CustomerName = (string)row["CustomerName"]
                                       }).ToList();
            }

ACTION:

public async Task<ActionResult> Index()
        {
            var watch = System.Diagnostics.Stopwatch.StartNew();
            List<CustomerModel> model = new List<CustomerModel>();
            CustomerRepo2 aa = new CustomerRepo2();
            await aa.GetAllCustomers();
            await aa.GetAllCustomers();
            await aa.GetAllCustomers();
            watch.Stop();
            var elapsedMs = watch.ElapsedMilliseconds;
            ViewBag.time = elapsedMs;
            return View();
        }