1 Premium day ?

[czezz]

I have this coin - 1 premium day - and it says that it gives 50% XP more from adventure and so on.

I am going to start adventure which will take me 2-3 days to complete.
So my question is:
Should I activate 1 premium day just before I start adventure OR just before I finish adventure to get premium bonus ?

[corona88]

Before you finish.

Premium must be active when you finish adventure.