Hi nicko96 - Are you having a character consume your new potion from a skill, or just from their inventory?
If from inventory, I'm not sure if there's a way to make the effect last multiple 'turns'.
From a skill, I think you can set the skill properties to something like:
CONSUME,100,2,FOOD_Bread
(where 2 is the number of turns to apply; and 'FOOD_Bread' is the name of the item to consume from the Stats > Potion table) I believe that should apply the consume effect to multiple rounds like you want.
What's your end goal / the context of what you're trying to achieve?
Good luck!