The root cause is identified_time is set only once when heuristic analysis is completed. Since try jobs run after heuristic analysis and are necessary to have results for auto revert, using identified_time is too early. Updated_time is set once try job results are complete and is more accurate for measuring against sheriff_updated_time

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/6b4faa1189acf650a519c0737fa72f5af93dc1e6

commit 6b4faa1189acf650a519c0737fa72f5af93dc1e6
Author: Jeffrey Li <lijeffrey@chromium.org>
Date: Wed Apr 05 18:29:16 2017

[Findit] Auto revert metrics - use cr_notification_time instead of identified_time

Bug:  703859 
Change-Id: Ic56b7f616483ceb8ab39ab5df62ec70b5c900252
Reviewed-on: https://chromium-review.googlesource.com/468448
Reviewed-by: Chan Li <chanli@chromium.org>
Commit-Queue: Jeffrey Li <lijeffrey@chromium.org>

[modify] https://crrev.com/6b4faa1189acf650a519c0737fa72f5af93dc1e6/appengine/findit/handlers/auto_revert_metrics.py
[modify] https://crrev.com/6b4faa1189acf650a519c0737fa72f5af93dc1e6/appengine/findit/handlers/test/auto_revert_metrics_test.py