Noun clause/adverbial clause

Dear friends,

My friends and I disagree on whether the following sentence is correct or not:

When I get home is late.

To me, it seems - actually I am %100 sure - that this sentence is wrong. "when I get home" is an adverbial clause of time, and the rest is the independent clause, which means it needs a subject - here the dummy subject it.

And then there is this friend of mine who goes: "when I get home" is a noun clause which functions as the subject here. He reasons that it can be replaced by "it" and whatever can be replaced by "it" is a noun clause.

I think this clause can function as a noun clause in sentences like the following"

When I get home is none of your business.

So, it is the context, semantic properties of the words like "late" being part of it, which is the determining factor.

I should be more than grateful if you could help us find the correct answer.