I know this thread is kinda old already but I figured an update wouldn't hurt for others who might face a similar situation.
I took a flight from TBS - IST on Turkish and got on that just fine today. I got to Istanbul at around 6AM and had to wait 'til 9:30AM so I could check in at the ticket counter for a 12:30PM departure.
I checked in and was told they couldn't give me a seat assignment 'til 11:15AM (when check-in closes) due to possible cargo restrictions (Deltanet has an advisory on it).
The loads were 14 Business and -4 Coach.
I managed to get a seat in Business for the flight. The other 9 nonrevs/buddy pass guys also got on.
I figured if I couldn't get on this flight today, I'd try the 10AM flight w/ Turkish the following day...and if that didn't work out, I could give the Delta flight another shot at 12:30PM the following day, as well.
Like others had warned, though....they don't give out "Seat Request Cards" so you can pass security/passport control, only seat assignments until they're positive you're getting on (all this at the ticket counter). That means you have to rush through passport control and onto the gate. It got kinda tight today and had to run a bit.
Thanks for all who helped out and especially to those who wrote me the long PMs.