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Can I make an event recur on the fifth week of a month?

Only first to fourth week and last week is possible for monthly recurrence with the Custom Recurring Events add-on. It is not reliable otherwise, since there is not a fifth week on every month. Our recurrence options are modeled after the same schema as Google Calendar and Apple Calendar in this way. You would need to move the date forward manually or add multiple events for a fifth week recurrence.