[1] From what I've read in the official documentation the timeline is foremost filled based on external services. Using the Pebble app you have to subscribe to a service, after which your subscription will be registered by Pebble (the company/website). The external service then has to push the pins to Pebble (company/website), after which the Pebble app will then query Pebble (company/website) for all new/updated pins and push those to the watch itself.