What is the likely benefit of earlier thrombolysis?

Theory, experiment, and common sense all suggest that the earlier thrombolysis is given for acute myocardial infarction, the greater should be the benefit. We would expect the time-effect, i.e. the increased efficacy of thrombolytic therapy with earlier administration, to be very powerful, and of immense clinical importance. However, from randomized clinical trials it appears that the benefit of earlier thrombolysis is only very modest. The results of clinical trials, therefore, apparently conflict with our expectations based on theory and experiment. How can this be explained?