This first part was released earlier, and copied here so that if you have not read everything, you get all the information as it came out. I also want to remind everyone that until we get an official GW announcement, everything is classified as rumors.
Whoa!. I had to read it like 3 times before it sank in........ Hold the phones, stop the press, just wow. I was happy on the first line, sad on the second line, then held in suspense, and then crying at the end.
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).
Updated with More Information to clarify pre-orders and release dates.
The 25th is the white dwarf which is all about the new starter and chaos space marines.
Pre-Orders for the new starter set begin on the 25th, for release on the 1st.
Pre-Order for Chaos Space Marines go up on the 8th and the entirety of their range will be released in two waves on the 15th and the 29th.