Abstract. In a previous paper, we defined TURTLE, a Timed UML and RT-LOTOS Environment which includes a real-time UML profile with a formal semantics given in terms of translation to RT-LOTOS, and a model validation approach based on the RTL toolset. This paper presents an enhanced TURTLE with new composition operators (Invocation, Periodic, Suspend / Resume) and suspendable temporal operators which makes it possible to model scheduling constraints of real-time systems. The proposed extension is formalized in terms of translation to native TURTLE. Thus, we preserve the possibility to use RTL to check a real-time system model against logical and timing errors. A case study illustrates the use of the new operators.