def now(latency: Optional[datetime.timedelta] = None) -> Perf:
        """Create a `Perf` instance starting now and ending now plus latency.

        Args:
            latency: Latency in seconds. If given, end time will be now plus
                latency. Otherwise end time will be a minimal interval plus start_time.
        """

        start_time = datetime.datetime.now()
        if latency is not None:
            end_time = start_time + latency
        else:
            end_time = start_time + datetime.timedelta(microseconds=1)

        return Perf(start_time=start_time, end_time=end_time)
Create a `Perf` instance starting now and ending now plus latency.

        Args:
            latency: Latency in seconds. If given, end time will be now plus
                latency. Otherwise end time will be a minimal interval plus start_time.
        
src/core/trulens/core/schema/base.py