time spent difference between rknn.inference and rknn.eval_perf

I ran 100 times of  rknn.inference() of mobilenet-v1-ssd and measure average time of each run using time.time(). It is

Time:  0.0248 sec

However, rknn.eval_perf() shows:

========================================================================
Total Time(us): 13779 (0.013779 sec)
FPS: 72.57
========================================================================

Both has the same input image, How can rknn_eval time be almost half of rknn.inference? Which one is more accurate?

Thanks,