The European IST project Interval (1999–2002) focused on coherent timed extensions for the ITU-T modeling languages SDL, MSC, TTCN. In the case of SDL, a set of extensions were defined and proposed to ITU-T in order to be a basis for a new recommendation. This paper gives a short overview of these extensions, and describes which enhancements were achieved on an SDL prototype tool in order to make it possible to use these extensions. For a more detailed description of these extensions see [1]. Finally we present an industrial-size experiment on an IETF protocol with the purpose of validating three things: accuracy of SDL time extensions, usefulness of the enhanced tool, and correctness of the protocol itself.