[Hummingbird] Browser caching panel in dashboard shows Fatal error: Uncaught Error: Unsupported op

With Hummingbird Pro on a multisite install at the network level, the dashboard page has a pane for Browser caching, which shows the following error:

Fatal error: Uncaught Error: Unsupported operand types in /home/inrs/public_html/wp-content/plugins/wp-hummingbird/core/class-utils.php:686 Stack trace: #0 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/class-dashboard-page.php(585): WP_Hummingbird_Utils::human_read_time_diff(Array) #1 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/views/meta-box.php(31): WP_Hummingbird_Dashboard_Page->dashboard_browser_caching_module_metabox() #2 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/abstract-class-admin-page.php(125): include('/home/inrs/publ...') #3 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/abstract-class-admin-page.php(295): WP_Hummingbird_Admin_Page->view('meta-box', Array) #4 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/views/wphb-page.php(11): WP_Hummingbird_Admin_Page->do_meta_boxes('box-dashboard-l...') #5 /home/inrs/public_html/wp-content/plugins/wp-hummingbird/admin/abstract-class-admin-page.php(125): include('/home/inrs/publ...') #6 in /home/inrs/public_html/wp-content/plugins/wp-hummingbird/core/class-utils.php on line 686