Singular vs Plural – Is ‘Series’ Plural or Singular?

I'm a statistician. "Variance of waiting time" is how I would word this and how I have seen it worded elsewhere. This is similar to other uses of variance. We say the "variance of weight" or "variance of income" etc.

So, "of" and singular.

This is largely stylistic. Typically they would be singular. (Name, Address, etc.) However, your "Parameter name" entries have multiple parameters names, so you might show that with the headings:

| Parameter category | Parameter names |

or: (if there may be any number of parameter names)

| Parameter category | Parameter name(s) |