It is a very broad topic.
For time-series analysis I would choose one of the sections on probability and statistics.
For deterministic dynamical systems I would go to differential equations.
If the question strongly depends on specifics of a particular field (such as economics), I would perhaps go to the corresponding section instead.
In any case, if you choose a section that you think is correct, but it turns that your question is better placed in another section, it will probably be moved there without much difficulty.