Can I not use functions such as math.min and math.max in the function node?

Yes, those functions are available in the Function Node. But, it’s going to be `Math.min()`

not `math.min()`

(capital). Here are the docs for reference:

I tried that earlier, but just figured out that I had to use this syntax:

payload.data.min = Math.min.apply(Math,payload.data.timeSeries);

and not just payload.data.min = Math.min(payload.data.timeSeries);