I am trying to see if the colloquial usage of night and day is non-standard and is improper register, or if it is simply an ommitted definition in the dictionaries:
night and day: Describing a contrast between two completely different things, often one that has resulted in improvement. Often preceded by "like."
The context is from an interview where a person talks about a course where she learned a lot:
I loved the course. Life was totally different. It was just night and day.
This question already covers quite some discussion about the matter: Is the usage of “night and day” as “completely different” very common?
However it does not clarify if this is non-standard or should be avoided. It struck me that none of the standard authoritative dictionaries I checked (about 10 of them) even mention this definition of the idiom, only the "continually" meaning, so I started to wonder if this usage is frowned upon on non-standard.
I have heard it countless times in spoken English, but I would expect it to be in a dictionary at least, mentioning it is spoken as needed. But in addition to the slang/idiom dictionaries mentioned in the linked post, I found it only on The Free Dictionary also in its idiom section only, the definition I pasted above. The definition mentions that it is often preceeded with "like", which is also mentioned in the accepted answer to the linked post.
Does somebody actually know a dictionary definition? Does someone have an explanation why is it not listed as a definition in any of the main dictionaries? And does this missing definition mean that it should not be used in proper speech/writing?