Survivor premieres on September 19th this time around, and that's a month from today, In the past CBS has usually starting releasing casts about 3-4 weeks ahead of premieres, which in Survivor's case would be the last week of August or just after Labor Day (which is September 3rd this year.) For TAR that time frame would be around that same weekend (September 1-2-3) or that week following that weekend.
But with the political party conventions coming as late as I've ever seen (August 27-30), (September 3-5) and with the Olympics having been later than average (running into August 3) and with most of the new shows and new seasons premiering between the 24th and 39th, it's hard to be sure if they'll start announcing casts for Survivor and TAR as far ahead as normal. But I agree that Survivor will be first, and TAR is likely to be about 10 days later.