The disclosure relates to testing software for operating an autonomous vehicle. For instance, a first simulation may be run using log data and the software to control a first simulated vehicle. During this, one or more characteristics of the simulated vehicle may be compared with one or more characteristics of a vehicle from the log data. The comparison may be used to determine a divergence point for starting a timer. In addition, a second simulation may be run using the log data and the software to control a second simulated vehicle. The divergence point may be used to determine a handover time to allow the software to take control of the second simulated vehicle. Whether the software is able to continue through the first simulation before the timer expires without a particular type of event occurring and/or the second simulation without the particular type of event occurring is determined.