first click to reach CiviCRM dashboard results in long delay and error message
I updated the Drupal core to version 7.54 using "drush upc", which reported pending database updates, so I also did "drush updatedb".  The Drupal core update also caused several "projects" to be updated as well.

All of this seems to have cleared the problem I originally reported – I no longer see a long delay when I first log in and click CiviCRM.