The 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language, would consider words like yesterday, today, tonight, and tomorrow as pronouns (specifically, deictic temporal pronouns). Related info is in CGEL pages 429, 564-5.
Can you do it for tomorrow? Vs Can you do it by tomorrow? Can you do it for tomorrow? —From Collins dictionary Why I should choose "for" in place of "by"??
I have been poking around wondering about the colloquial usage of on tomorrow in Southern American English and wondering about its origins. I can find some records of official usage of the phrase i...
american english - Origins and history of "on tomorrow", "on today ...
The contraction "tomorrow's" is used to mean "tomorrow is" all the time. Just search for "tomorrow's going to" to find all manner of examples.
grammar - Is "Tomorrow's" equal to "tomorrow is"? - English Language ...
Tomorrow morning is idiomatic English, tomorrow's morning isn't. Night sleep doesn't mean anything in particular - you have had a 'good night's sleep' if you slept well all the previous night. So there is no pattern to whether or not you use an apostrophe.
I think it is a good question. When there is yesterday morning and tomorrow morning, why have an exception for this morning (which means today's morning)? Yes, idiom, but I actually do like idiomatic extensions like these - as long as everybody knows what is meant and no grammar or semantic rules are violated...