I would ditch the wired release and use the interval timer in the camera menu. It so happens I use a D7000, and in a quick-and-dirty trial just now, setting my shutter speed to 30 seconds, I got 5 shots with the interval set to 33 seconds. I tried 31, then 32, but the next frame didn't fire until the next interval counted. At 33 it fired consecutively, and was still just less than a second after the previous frame. I can't explain the timing unless one of the clocks (shutter timer or interval timer) is off somehow, as I didn't actually put a stopwatch on it. But then I remembered to turn off auto-focus, thinking the focus function was what delayed the next frame, but it still fired almost immediately, but only with a 33-second interval.
Anyway, I could get just under two frames per minute with minimal closed-shutter time between frames, and I have no reason to think I couldn't set it to do 999 of those, which is certainly more time than the battery will run!
If you want the frames to be 30 seconds apart, which would make time calculations easier after the fact, then set a 30-second interval on a 25-second shutter speed. That makes just a bit longer gap between frames, but still only 4 seconds or so.