Cocktail.Schedule.add_exception_time

You're seeing just the function add_exception_time, go back to Cocktail.Schedule module for more information.
Link to this function

add_exception_time(schedule, time)

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Specs

add_exception_time(t(), Cocktail.time()) :: t()

Adds an exception time to the schedule.

This exception time will cancel out any occurrence generated from the schedule's recurrence rules or recurrence times.