With the newer versions of Codeception, the internal variables have declared types. So whatever extends the abstract class Module (like Clock) needs to have it declared too. Otherwise, this error appears:
PHP Fatal error: Type of JeckelLab\Clock\CodeceptionHelper\Clock::$config must be array (as in class Codeception\Module) in /var/www/project/vendor/jeckel-lab/clock/src/CodeceptionHelper/Clock.php on line 25