class_docstr: A timer that tracks a duration since creation.
class_docstr_tok: ["A","timer","that","tracks","a","duration","since","creation","."]
code: def __init__(self, duration_secs):
      self._start_time_secs = time.time()
      self._duration_secs = duration_secs
  
imports: import time
  from typing import Optional, Tuple
  import numpy
  from tensorflow.python.checkpoint import checkpoint_management
  from tensorflow.python.client import session
  from tensorflow.python.distribute import distribute_lib
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import ops
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.training import saver
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 1 to create a new _CountDownTimer object  with example: obj = _CountDownTimer(duration_secs)