Is My Teacher's Sentence Correct?

Hi,

Today my English teacher wrote a sentence to the board. I told her that I think the sentence is incorrect but she told me there isn't anything wrong with the sentence. After that I tried to find sentences with same grammer but i couldn't.

The sentence:

"The last time he shaved his beard was two days."

and he wanted another student to rewrite it as:

"He hasn't shaved his beard for two days."

The second sentence is correct but what about the first one? Are there any grammer which allows you to use "was two days" without something like "ago"?