Premium tokens are not automatically activated when you buy them.

To activate a premium token:

1. Open the Card screen
2. Click on Buy Premium Token. Any unactivated Premium tokens will be shown on the top left of the screen
3. Click on the Premium Token you wish to activate

Once it is activated it will show on the right top of the screen with a timer showing how much time is left on it. Just like cards, once a premium token is active on a particular game world, it is only active on that game world, not across all game worlds.