Is the Cresselia Incense usable outside of the event?

I went months without proper sleep tracking because my Fitbit stopped syncing with my phone. Finally got a new one on Sunday, and after my first sleep with it, I got Darkrai.

However, I'm in Taupe Hollow, and it says I can't use the Cresselia Incense. (Grabbed one during the event.) Is it just because of the research area, or is it just unusable after the event? Serebii lists all of the locations for where you can find one.

Thanks!