It’s a 5-minute walk. - no problem It’s 5 minutes’ walk. - no problem . Interesting. It might be a regional difference. New Zealand English (generally close to British) or maybe I'm just uncouth and uneducated :( Enjoy.

No, you need the article 'a' to have the proper syntax when using 5-minute walk. 'It is a 5-minute walk' or 'It will take 5 minutes to walk' would be another acceptable choice. In the first phrase, '5-minute walk' is a noun and in the second phrase 'walk ' is a verb so 5 minutes is an adverb describing the verb walk.