Here's what I think gets confusing to people. The camera has all the information it needs to do what you want it to do the minute you press the shutter button to start the process, so why doesn't it do what you want? The next thing it will do after you start the interval process is depress the shutter, so it knows about long exposure NR, and if you're in Shutter priority it knows about exposure time (it can't in the others). The real problem lies in the question of "What is an interval?" Does a "10 second interval" mean that a photographer wants a photo every 10 seconds, or that they want 10 seconds between every photo? There are practical applications of each, and it would be great if the interval function gave you the option of setting it either way - but it doesn't.
Nikon has implemented the first way - a 10 second interval means that the shutter is depressed every 10 seconds. What's not taken into account is whether the camera is ready for another shot or not, so
unready camera actuations are counted but ignored. In other words, it counts the fact that it's depressed the shutter and doesn't care whether the camera was ready or not.
So, you set the camera for a 30 second exposure and have Long Exposure NR on. You set a 10 second interval time, ask for 10 intervals with 1 shot per interval, and want it to start now. Here's what happens as you press the press the shutter ...
Interval 1 (00:00) : Shutter actuates for first exposure
Interval 2 (00:10) : actuation ignored - shutter is still open from first exposure
Interval 3 (00:20) : actuation ignored - shutter is still open from first exposure
Interval 4 (00:30) : actuation ignored - shutter closes from first exposure and begins Long Exp NR
Interval 5 (00:40) : actuation ignored - Long Exp NR processing from first exposure running
Interval 6 (00:50) : actuation ignored - Long Exp NR processing from first exposure running
Interval 7 (01:00) : (A) actuation ignore - Long Exp NR processing from first exposure running, or (B) 2nd photo starts
Interval 8 (01:10) : (A) 2nd photo starts, or (B) actuation ignored - shutter is still open from second exposure
Interval 9 (01:20) : actuation ignored - shutter is still open from second exposure
Interval 10 (01:30) : (A) actuation ignored - shutter is still open from second exposure, or (B) actuation ignored - shutter closes, 2nd exposure begins Long Exp NR
... timer finishes, and you've got 2 photos where you expected 10. It would have been great for the camera to do a quick calculation and let you know that your interval time was too short, but it's a camera, you're the photographer, and it's going to do the best with what you provide it. It would be nice if it at least not tick the shot off the total count if the shutter did not actuate.
I have a Vello wired remote that will do infinite intervals (i.e. more than the 999 I get with the D600 & D7000). It has no way of knowing the answers to questions 2 and 3 above so cannot factor in when the interval actually ends, so all it does is actuate the shutter and begin a countdown, just like the camera. If you wanted it to do 10 seconds between shots you would need to know that the camera requires 30 seconds for each exposure and 30 seconds for noise reduction before it will be ready to actuate again. So, to get 10 seconds between shots you need to calculate...
Interval Time = Shutter speed + Long Exp NR Time + The Amount Of Time You Want Between Shots
So in our example, to get 10 seconds between shots the interval time needs to be set to 70 seconds (01:10).
VectorZ, I'm not sure why you're only getting 11 shots and would need to know 1) how many intervals you were asking for, 2) what shutter speed were you using, and 3) did you have Long Exposure NR on? If I know your settings I can tell you precisely why you got what you got, and what you would have needed to do to get it to do what you really wanted.