code: def calc_elapsed_time(self):
      for key, (start_time, end_time) in self.key_to_times.items():
          elapsed = end_time - start_time
  
          if key not in self.results:
              self.results[key] = []
  
          self.results[key].append(elapsed)
  
imports: from __future__ import absolute_import
  import csv
  import os
  import time
  from collections import OrderedDict
  from contextlib import contextmanager
  from importlib import import_module
  import numpy
  from nnabla.ext_utils import import_extension_module
  from .base import FunctionHookCallbackBase
label_desc: Use image node_id 5 for calling the CpuTimerCallback obj's underlying member method code with example usage: obj.calc_elapsed_time() without return types