message: Write start time, end time, and duration to benchmark results
diff: +import time
  +
  from absl import app, logging
  from autofl.datasets import (
  @@ -55,9 +57,10 @@ def benchmark_ul_fl_FashionMNIST_10p_5400():
  def _run_unitary_versus_federated(name: str, xy_splits, xy_val, xy_test, C):
  - # TODO train n models on all partitions
  + start = time.time()
  # Train CNN on a single partition ("unitary learning")
  + # TODO train n models on all partitions
  partition_id = 0
  logging.info("Run unitary training using partition {}".format(partition_id))
  ul_hist, ul_loss, ul_acc = run.unitary_training(
  @@ -74,6 +77,8 @@ def _run_unitary_versus_federated(name: str, xy_splits, xy_val, xy_test, C):
  xy_splits, xy_val, xy_test, ROUNDS, C=C, E=FLH_E, B=FLH_B
  )
  + end = time.time()
  +
  # Plot results
  # FIXME use different filenames for different datasets
  report.plot_accuracies(ul_hist, fl_hist, fname="UL-FL-plot.png")
  @@ -81,6 +86,9 @@ def _run_unitary_versus_federated(name: str, xy_splits, xy_val, xy_test, C):
  # Write results JSON
  results = {
  "name": name,
  + "start": start,
  + "end": end,
  + "duration": end - start,
  "FLH_C": C,
  "FLH_E": FLH_E,
  "FLH_B": FLH_B,
  