code: def on_train_batch_start(
      self,
      trainer: Trainer,
      pl_module: LightningModule,
      batch,
      batch_idx: int,
  ):
      self.step_start_time = time.time()
  
file_path: NeMo/examples/multimodal/x_to_nerf/benchmark_callback.py
imports: import time
  from typing import Optional
  from pytorch_lightning import Callback, LightningModule, Trainer
  from nemo.utils import logging
label_desc: Use image node_id 5 for calling the BenchmarkCallback obj's underlying member method code with example usage: obj.on_train_batch_start(trainer, pl_module, batch, batch_idx) without return types