Twelve Full Screen Transition Speed

According to the Twelve theme documentation there is a _showFullscreen option that you may set to false to disable the fullscreen button.
Just edit the option set you're using in the Drupal module and at the bottom of the option set table, use the text input field next to the select box to add the _showFullscreen option. You can then set this option to false to disable the fullscreen button.

To change the transition effect when in fullscreen, have a look at the fullscreenTransition option. Valid values may be found here.

Please report back if I could help you and close this issue if so.