I was admitted to BCS a couple years ago on the cognitive side, and got an invite in December, as did a couple other cog people I know (not sure if we were "clear admits"--is this based on insider info or inferring based on grad cafe search results [not being snarky; genuinely curious]). Others I know got invites in January.
And yes (to another person's question) invites are handled separately by track (to some degree), as are admission decisions more generally.