do sometimes omit on in time expressions in informal English,
although I think it is more characteristic of American English than
British English. So in your first example, Anid, both versions are
possible. Compare the following:
will meet on Sunday next week.
will meet Sunday next week.
wedding anniversary is the 22nd of October.
wedding anniversary is on the 22nd of October.
going to have a game of tennis Wednesday evening.
going to have a game of tennis on Wednesday evening.
that if we say: Ill see you next Sunday week rather
than Ill see you Sunday next week, it is not the following
Sunday that is intended, but the one after that!
your example of a time expression with the past tense, I
think we would normally use one of the following formulations:
happened last Friday.
happened on Friday.