Unsure whether the clause in this sentence is restrictive or nonrestrictive [closed]

In a comment, John Lawler wrote:

The comma in writing, and the comma intonation in speech, mark it as a nonrestrictive relative clause modifying these times. The distinction between restrictive and non-restrictive relative clauses is a syntactic one, and depends on intonation and relative pronoun choice (you can't use that with a non-restrictive relative, but you can with a restrictive), not some vague notion of "making sense". That's not grammar.