When do obsolete branches get deleted?

Just started using Neon. For the time being we're going to keep our prod db elsewhere, while using Neon for dev and feature branches (i.e our dev branch is our primary branch). Our app is deployed in Vercel and we've successfully installed the integration (had to manually update the DATABASE_URL set by Neon in the Vercel env vars to point to Preview and not Production, but otherwise quite smooth). What I'm wondering about is when do branches get deleted? I push a new feature branch, Vercel is building it in a Preview env, a Neon branch is created, I open a PR, merge it, then delete that feature branch, but the corrosponding Neon brandh doesn't get deleted. That's even though it is marked as OBSOLETE in the "Vercel integration" panel, and the "Automatically delete obsolete Neon branches" option it turned on.