This might one day have my whole config but at the moment I have only posted my garden irrigation system which is (almost completely) a self contained package.
See here for more information - https://community.home-assistant.io/t/my-garden-irrigation/99686
5 April 2019 - Corrected the logic for updating next run time.
31 March 2019 - I have added a script to garden_irrigation.yaml that sets pulsetime[1, 2, 3, 4] on the Sonoff to act as a failsafe in the event that HA loses any communication with the switch.
Thanks to @itajackass for finding the Sonoff command.