The label on that textbox really doesn't make sense for anything other than a gif. Either that or having frame numbers on the timeline is just confusing.
In any case, here's now it works right now:
The timeline shows frame numbers as if the animation were 30 fps. The reality of it is that 30 marks one second. 60 marks two seconds. It doesn't really mean frames per se like it would on a system like Flash or something, because, like in-game 3D systems, Spine renders per update and your computer will usually render much faster than 30 fps.
Also note that the numbers land on lines instead of in between lines, and also starts at 0. This reflects the system accurately, that keys are at points in time and not for discrete frames.
Exporting one second of animation at 15 fps results in 15 exported frames. Exporting two seconds of animation at 15 fps results in 30 exported frames.
If you were to export at 30 fps, the number of exported frames would be equal to the numbers on the timeline.
So, in short, maybe you want to put 30 in the box.
