Once parameters (up to 4) for "Default Unique ID" are set, go to "Tracking" tab on offer detail page and turn  " Limit Conversion by Unique ID" ON;
At network default time zone conversion will be recorded only once within 24 hours according to Unique ID rule. All subsequent clicks within the same day will be marked as  "Rejected" in Conversion Report.
For example, if Unique ID is based on Offer,Affilaite,IP,s2 (transfer sub affiliate's value). It means  at the network time zone within 1 day only a first conversion which is meet these rule requirements will be approved,  all subsequent conversions will be rejected.