Understanding Transition faults
You are confusing two different ideas. Timing convergence during the design cycle will detect design errors, which can be corrected during the design process. A transition fault is a fault that occurs during manufacturing or operational use, such as a poor contact that has abnormally high resistance or a wire that is too narrow. You want to be able to detect these faults in your acceptance test, which the test you run on manufactured devices. The acceptance test procedure is usually much different from the functional test that you use in the design cycle, and there is an incentive to make the acceptance test as short as possible to save money during testing.