wp_schedule_event will not accept class hook

[jonshipman]

wp_schedule_event will not accept array() for the hook (must be string). As such, wp_schedule_event( time(), 'daily', array($this,'hook') ); will not work, however, moving the hook method outside of the class will work as the $hook is no longer an array.

[TobiasBg]

You are mixing up "hook" and "callback" here.
wp_schedule_event indeed requires a string as the "hook", in the sense of plugin action hook. You can then attach a "callback" (usually a function or class method) to that action hook:

wp_schedule_event( time(), 'daily', 'my_unique_plugin_event_hook' );
add_action( 'my_unique_plugin_event_hook', array( $this,'hook' ) );