Sure, you just have to type the same code 91 times...
As you can guess, that's not a viable approach. If you start numbering variables, you're doing it wrong.
If you're on R2018b or later, it's trivial to obtain your vector:
Optionally, you can squeeze the result, but having a vector along the page makes more sense.
In earlier versions, var can only operate on one dimension at once, so you must first reshape your matrix into an Nx91 matrix:
V = var(reshape(B, , size(B, 3)))