Is it correct to say second maximum?
In my experience "maximum" refers to a singular value. In calculus you can have "local maximum" of a curve that is not the global maximum of the curve.
In statistics, however, you can rank values. You can have a "highest rank" and "second highest rank". But even there I don't hear "second maximum" as a common phrase.
There is also "sub-maximum" but I hear it in things that aren't easily counted. "He gave a sub-maximal effort".