The complexity of automation and control systems is fast increasing in order to satisfy the arising needs of the manufacturing industry. The central exigencies for new production facilities are flexibility, adaptability and reconfigurabilty in combination with guarantees for downtime less operation. Additionally modern automation systems are supposed to execute control applications distributed across heterogeneous networks The standard IEC 61499 introduces a function block oriented architecture which should be able to satisfy most of these new requirements. Still some of the open issues within the standards definition are the consideration of real-time constrained applications, the missing possibilities and conventions to define an explicit execution order and the absence of an appropriate modelling technique for real-time constraint specification. Therefore the main topic of this paper discusses investigations on possibilities to define execution order and real-time constraints in IEC 61499.