Editing credit set date to match payment date

No, there is no third date when applying a credit memo to an Invoice.  There is also no payment involved.

Though you can record a payment and apply a credit at the same time, the application of the credit and the  payment transaction are not connected.

Quickbooks treats applied credits like payments so if the application date doesn't match it will look like a "payment" is showing up in the wrong period. This is a creating a problem for me when I am trying to calculate sales commissions based on payment date.  

The customer is electing to take the credit on a specific day not necessarily on the date that the invoice is generated and the application should reflect that. 

Well, that's an idea, but there's no way to do that.

There wouldn't be a third accounting date, in any case. Any third date would be more like a memo.

The Invoice has a date. The Credit Memo has a date. There is no other accounting date, as there are just the two transactions.

Yes, there is an application date when the transaction happens that counts as a payment being applied regardless if it is cash or it is a credit memo so I am not sure why the functionality to change the date is not there.