We present an extension of synchronous programming languages that can be used to declare program locations irrelevant for verification. An efficient algorithm is proposed to generate from the output of the usual compilation an abstract real-time model by ignoring the irrelevant states, while retaining the quantitative information. Our technique directly generates a single real-time transition system, thus overcoming the known problem of composing several real-time models. A major application of this approach is the verification of real-time properties by symbolic model checking.