Hi Aislan,
I guess your query is regarding the due date in accounting line items, so that is reflects currectly in the cash flow, i guess more to do with customer ageing.
You can manually change the "base line date"in the accounting document, double click on the accounting line item, and you can change the base line date.
You need to check with your FI consultant for that, If this solution is not accepted then i think you will have to do a devlopment effort. Also i am sure you are aware that each milestone can have a different payment term.
Let me know your response on the same.
Regards
Aadesh
