We’ve had similar real world situations (components subscribing to external information) and at the moment you simply can’t encapsulate it without using private Phoenix LiveView APIs. We just bit the bullet and have the parent live view do a handle_info to send_update.

However, I believe there are plans to allow send_update to work from external processes which would allow you to ping the component directly.

I had another look at this, re-implemented as a LiveView, and everything is much simpler.

defmodule MyApp.ClockLive do
  @moduledoc """
  Renders a live clock that updates at a periodic interval.

  The clock update frequency (`interval`) and the output format (`strftime`)
  are configurable session options.

  To call from the parent template:

      <%= live_render(@socket, MyApp.ClockLive, id: 1, session: %{"interval" => 10_000}) %>
      <%= live_render(@socket, MyApp.ClockLive, id: 2, session: %{"strftime" => "%H:%M"}) %>

  """

  use Phoenix.LiveView

  @impl true
  def mount(_params, session, socket) do
    start_timer(session["interval"] || 1000)
    strftime = session["strftime"] || "%H:%M:%S"
    state = [strftime: strftime, date: local_date(strftime)]
    {:ok, assign(socket, state)}
  end

  @impl true
  def render(assigns) do
    ~L"""
    <%= @date %>
    """
  end

  @impl true
  def handle_info(:clock_tick, socket) do
    newdate = socket.assigns.strftime |> local_date()
    {:noreply, update(socket, :date, fn _ -> newdate end)}
  end

  defp start_timer(interval) do
    :timer.send_interval(interval, self(), :clock_tick)
  end

  defp local_date(format) do
    NaiveDateTime.local_now()
    |> Calendar.strftime(format)
  end
end

I wrote a clock component, and ran into this self-updating issue too!

My solution also requires a handle-info handler in the parent LiveView…

defmodule MyApp.ClockComponent do
  @moduledoc """
  Renders a live clock that updates at a periodic interval.

  The clock update frequency (`interval`) and the output format (`strftime`)
  are configurable options.

  To call from the parent template:
  
      <%= live_component(@socket, MyApp.ClockComponent, id: 1, interval: 10_000 %>
      <%= live_component(@socket, MyApp.ClockComponent, id: 2, strftime: "%H:%M" %>

  To make this work, the parent LiveView needs a handle_info function:

      @impl true
      def handle_info({:tick, assigns}, socket) do
        send_update MyApp.ClockComponent, assigns
        {:noreply, socket}
      end

  The parent `handle_info` is required because there is no `handle_info` callback 
  for LiveComponent.  

  Ben Wilson (@benwilson512) on Elixir Forum says that in the future, there may
  be a `send_update` feature to allow external processes to ping the component
  directly.

  https://forum.elixirforum.com/t/livecomponent-updating-itself-at-regular-intervals/37047/6

  Also the code in the `update` callback is more complex than desired.

  Ideally the timer would start once in the `mount` callback.  This was not
  possible because the timer interval should be configurable in the assigns,
  and the assigns are not available in the `mount` params. (AFAIK)

  Maybe there is a simpler approach for starting the timer...
  """

  use Phoenix.LiveComponent

  @impl true
  def render(assigns) do
    ~L"""
    <%= @date %>
    """
  end

  @impl true
  def mount(socket) do
    {:ok, socket}
  end

  @impl true
  def update(assigns, socket) do
    opts = update_assigns(assigns) 
    unless assigns[:timer], do: start_timer(opts)
    {:ok, assign(socket, opts)}
  end

  defp update_assigns(assigns) do
    strftime = assigns[:strftime] || "%H:%M:%S"
    [
      id: assigns[:id],
      timer: "started",
      interval: assigns[:interval] || 1000,
      strftime: strftime,
      date: local_date(strftime)
    ]
  end

  defp local_date(format) do
    NaiveDateTime.local_now()
    |> Calendar.strftime(format)
  end

  defp start_timer(opts) do
    :timer.send_interval(opts[:interval], self(), {:tick, opts})
  end
end