If you pay whatever the delinquency amount is prior to the next billing due date, you have removed the account from delinquency status, and a new delinquency would then be determined based on when/if you thereafter become delinquent on the new billing.
You have a new date of initial account delinquency for any later delinquency once the account is brought back into a non-deliquency status by paying the current overdue amount.
Stated differently, the CRA credit reporting manual defines a reportable 30-late as an account delinquency that has extended 30 days past the last billing due date. It does not define a reportable 30-late based on having a debt for two payment cycles.
Generally (and this depends upon the creditor's accounting practices, but most companies follow the same guidelines) Payments are applied in the following order. Past due payment. Current payment, fees.
So If you pay the 250 from last month before it is 30 days late (note 30 days is 30 days, not 31.) You would not get reported as 30d. You would still get a new late fee for the current month.
If you pay 500, for last and this months rent, you would not be late anymore, but still have a 50 late fee on your account, but would not get an additional late fee for this month.
You can always call the creditor to check if this is the case.
Some CCCs won't report until it is 60 days late. PNC coems to mind. I would cal them and ask but don't give your name and CC account if you don't have to.