The Function list for a Date column is date-specific. It allows you to decide the type of modification you want to do on date values.
There are three different ways to generate the date value for duplicated records:
Modify date value: randomly selects the day, month or year to modify and puts a random value in place.
Switch day month value: switches the day and month values. If the original day value is greater than 12, then the new month value will be ((N-1) mod 12) +1. For example: If the original day is equal to 13, then the new month is equal to 1.
Replace by random date: generates a random date with day, month and year values.