For a software development project, management often faces the dilemma of when to stop testing the software and release it for operation, which requires careful decision making as it has great impact on both software reliability and project cost. In most existing research on the optimal software release problem, the cost considered was the Expected Cost (EC) of the project. However, what concerns management is the Actual Cost (AC) of the project rather than the EC. Treatment (such as minimization) of the EC may not ensure the desired low level of the AC due to the uncertainty (variability) involved in the AC. In this paper, we study the uncertainty in software cost and its impact on optimal software release time in detail. The uncertainty is quantified by the variance of the AC and several risk functions. A risk-control approach to the optimal software release problem is proposed. New formulations of the problem which are extensions of current formulations are developed and solution procedures are established. Several examples are presented. Results reveal that it seems crucial to take into account the uncertainty in software cost in the optimal software release problem; otherwise, unsafe decisions may be reached which could be a false dawn to management.