Expressions (phrases, clauses, etc.), Noun, Adverb (fukushi)
at the critical moment; when the time comes; when it's most important; when necessary; in an emergency; when push comes to shove
see いざ
いざというときのためにお金をためておきなさい。Put aside money for a rainy day.
Also written いざと言う時【いざというとき】