code: def end(self) -> None:
      assert self.start_time is not None
      self.duration += time() - self.start_time
      self.start_time = None
  
imports: from time import time
  from typing import Optional
  import torch
  import torch.distributed
  from coati.experience_maker import Experience
  from .base import Callback
label_desc: Use image node_id 3 for calling the Timer obj's underlying member method code with example usage: obj.end() without return types