It is an option of the Workflow action that, allows you to perform a Workflow action automatically at a specified time.
Remark: Availability of this option depends on your plan.
If you want create automatic action step, you need to:
(both fields must be filled in, otherwise the action won't be automatic)
Mark the checkbox in 'automatic execution'
enter the date in the field 'execution time'. The date must be in UTC format and must be a result of formula.
Remark: The option is not available for actions coming out of the start state