Should we include or leave out the preposition “on”

Question

Consider the following examples:

1. We are going to Japan on Wednesday.
2. We are going to Japan Wednesday.
3. We are going to Japan on tomorrow.
4. We are going to Japan tomorrow.

My question is about 2 and 3. For 2 I hear it spoken all the time, but it seems a bit unusual as written words. As for 3, the "on" feels very much a redundant word in both written and spoken English.

Wish that somebody could tell me if 2 and 3 are ok in terms of both spoken and written styles.

Answer 1

1, 2 and 4 are all acceptable American English.

3 is not.