Is it permissible to proceed with a contract to purchase an apartment from the Awqaf Authority, which includes an usurious condition (a 1% late fee on overdue installments), while being careful not to delay payment to avoid usury, or does the sin occur merely by the presence of the condition?

It is not permissible to enter into a contract that contains an interest-based condition, such as a late payment penalty, even if one intends to avoid incurring it, because the presence of an interest-based condition makes the contract forbidden. If the contract has already been concluded, and if it is possible to annul it, then that is obligatory. Otherwise, there is no harm in retaining the apartment, while being extremely careful not to delay in paying the installments.