How to handle condo association payment plans from delinquent owners

Some condo owners who are behind in their assessments have submitted repayment plans to the condo board. The amounts owed vary widely. The condo owners say they will pay a certain amount per month in addition to their regular assessments. This condo association is in Illinois. First, how do you decide whether to accept these repayment plans? Secondly, how long should we give these owners to pay what they owe? (What should the time frame be for these re-payment plans?)