If I turn on the maintenance mode in te WP toolkit and want to login I get redirected to the maintenance page. Can someone help me and explain how to turn on the maintenance mode and still be able to log-in to the WP admin page?
Such feature hasn't been implemented yet. So currently admin cannot login to admin panel when maintenance mode is enabled.
Corresponding Feature Request EXTWPTOOLK-962 has been created.
As a workaround, you can use WP Maintenance Mode plugin.