If something has gone wrong, for whatever reason, and you can't login because of the login cooldown, you can remove the cooldown by deleting a particular file.
- The file to delete is found within the plugin directory. This will likely be ....wp-content/plugins/wp-simple-firewall/
- The file name is mode.login_throttled
- Delete this file.
For more information about Login Cooldown feature, read the article here.