In this paper, we describe how the real-time verification tool UPPAAL has been extended to support automatic generation of time-optimal test suites for conformance testing. Such test suites are derived from a network of timed automata specifying the expected behaviour of the system under test and its environment. To select test cases, we use coverage criteria specifying structural criteria to be fulfilled by the test suite. The result is optimal in the sense that the set of test cases in the test suite requires the shortest possible accumulated time to cover the given coverage criterion. The main contributions of this paper are: (i) a modified reachability analysis algorithm in which the coverage of given criteria is calculated in an on-the-fly manner, (ii) a technique for efficiently manipulating the sets of covered elements that arise during the analysis, and (iii) an extension to the requirement specification language used in UP-PAAL, making it possible to express a variety of coverage criteria.