(a) When the court determines that a defendant must pay the costs of defense, the court may grant permission for payment to be made within a specified period of time or in specified installments. If no such permission is granted, the full amount shall be payable forthwith.
(b) When the court determines that a defendant must pay the costs of defense and the defendant is also placed on probation, or the imposition or execution of a sentence is suspended, the court may make payment of such costs a condition of probation or suspension of sentence.