Uncaught TypeError: gmdate(): Argument #2 ($timestamp) must be of type ?int, str

With v2.2.2 we’re seeing this from cron every few days:

PHP Fatal error:  Uncaught TypeError: gmdate(): Argument #2 ($timestamp) must be of type ?int, string given in WEBROOT/httpdocs/wp-content/plugins/woocommerce-wholesale-prices/includes/class-wwp-usage.php:470
Stack trace:
#0 WEBROOT/httpdocs/wp-content/plugins/woocommerce-wholesale-prices/includes/class-wwp-usage.php(470): gmdate()
#1 WEBROOT/httpdocs/wp-content/plugins/woocommerce-wholesale-prices/includes/class-wwp-usage.php(130): WWP_Usage->_fetch_effectiveness_data()
#2 WEBROOT/httpdocs/wp-content/plugins/woocommerce-wholesale-prices/includes/class-wwp-usage.php(562): WWP_Usage->get_data()
#3 WEBROOT/httpdocs/wp-includes/class-wp-hook.php(324): WWP_Usage->send_checkin()
#4 WEBROOT/httpdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#5 WEBROOT/httpdocs/wp-includes/plugin.php(565): WP_Hook->do_action()
#6 WEBROOT/httpdocs/wp-cron.php(191): do_action_ref_array()
#7 {main}
 thrown in WEBROOT/httpdocs/wp-content/plugins/woocommerce-wholesale-prices/includes/class-wwp-usage.php on line 470