The latest in the release schedule is here and I am not going to spoil it all by saying what it is.
This post has been updated with more information. Simply follow the link.
via Faeit 212 (a Must Remain Anonymous Source)
Chaos Space Marines is on the 8th of September
That said, the starter box will not be being released in September at all.
It's the last Saturday of August along with the White Dwarf previewing CSM. (the 25th).