Today I <work> <am working> <will work> from 9 to 8.

[loviii]

Good day!

My own examples:
Usually John works from 9 a.m. to 6 p.m., but tomorrow he decides to work from 9 a.m. to 8 p.m. Tomorrow has come. He wakes up at 7 a.m. and tells his wife Marry:
(1) Today I work from 9 to 8.
(2) Today I am working from 9 to 8.
(3) Today I will work from 9 to 8.

Are they all grammatical and if not, then why?
Do they all have a similar sense here and if not, then why?

Thanks!

 

[reno33]

Yes, they are all grammatical. Which one you would choose in actuality would depend on the exact context because they all have a similar sense.

 

[Uncle Jack]

You missed one. You can also say (4) "I will be working..."

Since the thing that most interests your wife is probably when you will be coming home, the most likely versions are (2) and (4).