Tidbyt heartbeats and device refresh rate

From https://tidbyt.dev/docs/build/authoring-apps:

Each Tidbyt regularly sends heartbeats to the Tidbyt cloud, announcing what it has cached. The Tidbyt cloud decides which app needs to be rendered next, and executes the appropriate Starlark script. It encodes the result as a WebP image and sends it back to the device.

I don’t see anywhere mentioned how often each Tidbyt sends “heartbeats” and I’m trying to determine which could be the refresh rate for the device.

My understanding is (please, correct me if I’m wrong) that each time the Tidbyt device sends a heartbeat to the cloud, it executes the script, and builds the image to send back to the device.

  1. How often does the device send heartbeats to the Tidbyt cloud?
  2. And, how the Tidbyt decides which app needs to be rendered next? Based on which criteria? It is a simple FIFO queue?