Every offer may have differing validation periods. Some are shorter, and some may be longer, depending on the type of industry.
In most cases, advertisers have a grace-period for consumers to return items they have bought as well as a period for any credit card fraud alerts to happen. This protects the advertiser from any losses and abuse from fraudsters, of which in this case conversions that are under this scenario are considered invalid.
Advertisers may take as fast as 14 days and as long as 60 days to validate a sale. If you are unsure of the validation periods, check the offer status or speak with your affiliate manager about it.