Exists in two variants: One is occupying the special inventory slot while the other is consumed as a buffing item and will display as a status icon:
To distinguish the difference, look carefully at the item description. The buffing potion will have a yellow written text labeled with 'Duration' and will always last 1 hour. The occupying potion lasts 3 hours.
When you use the occupying potion, you are able to deactivated it.
Both potions only consume time when you are online.
Only the buffing potion is stackable.
Cannot be activated with various items at the same time. Check out this page for more information: Combination of Buffing Items.
Currently it is unclear which box drops what potion.