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.
Question: What are the origins and history of using on tomorrow, on today, and on yesterday ** (which in standard Englishes are just tomorrow, today, and yesterday)? Examples: US Journal of the Senate (2006, all bold font added): ORDERS FOR ADJOURNMENT UNTIL 9 A.M. ON TOMORROW ...
american english - Origins and history of "on tomorrow", "on today ...
Today means "the current day", so if you're asking what day of the week it is, it can only be in present tense, since it's still that day for the whole 24 hours. In other contexts, it's okay to say, for example, "Today has been a nice day" nearer the end of the day, when the events that made it a nice day are finished (or at least, nearly so).
Today Was vs Today Is - English Language & Usage Stack Exchange
Neither are clauses, but "today in the afternoon" is grammatical (adverbial phrase of time), while "today afternoon" is not. I would also suggest "this afternoon" as a more succinct and idiomatic alternative to "today in the afternoon".
word choice - 'Today afternoon' vs 'Today in the afternoon'? - English ...
The phrase our today's meeting is commonly used in Indian English, even though other dialects of English frown upon it. The mentioned examples in the comments of our today's specials and our today's speaker will, I think, sound off to many speakers, but possibly not as much as our today's meeting.
Why is "our today's meeting" wrong? - English Language & Usage Stack ...
Which of the following is grammatical? What date/day is it today? What date/day is today?
Two other options (in addition to "as from today," "from today," and "effective today") are "beginning today" and "as of today." These may be more U.S.-idiomatic forms than British-idiomatic forms (the two "from" options have a British English sound to me, although "effective today" does not); but all five options are grammatically faultless, I believe.
Today had been the worst day of my life. seems awkward, as today is not understood to mean on this day (the original meaning). In narrative, an event that is happened in the past is narrated as it is the present, as in: It is the 1st of April, 2006. Today will be the worst day of my life. Outside that specific context, I would write
questions - "In which shift are you today? or In which shift you are ...
The fourth one is absolutely fine. As for other options, you could also use; His work is regarded as one of the highest peaks of Western culture today. Although this one is clunky and kind of implies a literal interpretation of "today" more than the other sentences. Personally I prefer option three the most.
Placing the adverb "today" in a sentence - English Language & Usage ...