To set a monthly recurrence on the Nth day each month, first set day and time, then set the recurrence by choosing the middle button from the toolbar on top, and the "<nth> day each month at <time>" option.
To set a monthly recurrence on the Nth day each month, first set day and time, then set the recurrence by choosing the middle button from the toolbar on top, and the "<nth> day each month at <time>" option.