class_docstr: The experience time metric.
  This plugin metric only works at eval time.
  
  After each experience, this metric emits the average time of that
  experience.
class_docstr_tok: ["The","experience","time","metric",".","This","plugin","metric","only","works","at","eval","time",".","After","each","experience",",","this","metric","emits","the","average","time","of","that","experience","."]
code: def before_eval_exp(self, strategy: "SupervisedTemplate"):
      super().before_eval_exp(strategy)
      self._time.update()
  
imports: import time
  from typing import TYPE_CHECKING, List
  from avalanche.evaluation import Metric, PluginMetric, GenericPluginMetric
  from avalanche.evaluation.metric_results import MetricValue, MetricResult
  from avalanche.evaluation.metric_utils import get_metric_name
  from avalanche.evaluation.metrics.mean import Mean
label_desc: Use image node_id 2 for calling the ExperienceTime obj's underlying member method code with example usage: obj.before_eval_exp(strategy) without return types