If you set up a payment plan and fail to make agreed payments, that will not reset the DOFD, and will not affect the credit report exclusion date.
The DOFD is a date-certain that is not affected by any payment or non-payment of the debt. It is fixed by the date of your first delinquency on the OC account, after which the account remained delinquent until either a charge-off or collection is reported. The additon of section 605(c) to the FCRA was with the express intent of removing any "reset" of the exclusion period for either a collection or charge-off based on anything other than the date-certain first delinquency on the OC account.
Agreeing to a payment plan and then becoming in default of that agreement can "reset" the SOL for purposes of the owner initiating civil action to seek a judgment. It provides a new "cause of action," and thus if you enter into a repayment plan, it can result in a new SOL.
SOL is unrelated to credit report exclusion of derogs.
As for affect of payment on credit score, yes, it can have some adverse effect, depending upon how long it has been since the last update by the creditor. A debt remains delinquent until paid, and once reported as paid, that effectively notifies the CRA that the debt was delinquent up to that date. FICO does consider that in its scoring. If the creditor updated very recently, then the scoring affect will be nil.
However, if it has been years since the last update stating that the account remains delinquent, then it can affect scoring.
Paying will terminate any future updated reporting that the debt remains unpaid, and thus will then permit the CO to begin to age.
If it remains unpaid, the creditor can make an updated reporting at any time, over which the consumer has no control.
