This will send an event called "focus_off" to Blink(1) whenever a FocusTime session starts. You will need to define a pattern for the "focus_off" rule on your Blink(1), and you most likely will want to create another recipe to handle the corresponding "focus_on" event when a FocusTime session is started.
Discover more time saving integrations for RescueTime and blink(1)