Why is the sentence below incorrect?
The mailman came at a time when it was impossible for me to get the mail.
While this construction is common in colloquial speech, the subordinate clause introduced by "when" is an adverb, so it can't modify the noun "time."
I think.
Steve is right.
If you substitute 'at which' for 'when,' the sentence will be fine.
The sentence "The mailman came at a time when it was impossible for me to get the mail" is incorrect because of a pronoun disagreement. The pronoun "it" is referring to the mail in the second part of the sentence, but the mail is not the thing that is impossible to get. Instead, it is the person who is unable to get the mail because of the time the mailman came. To make the sentence correct, you can rephrase it as:
"The mailman came at a time when I couldn't get the mail."
To figure out why the original sentence was incorrect, it's important to review the pronoun usage and agreement rules. In this case, it helps to identify the noun that the pronoun refers to and ensure that it matches in number and gender.