Correct, this is not in Oracle 12 and also not in the SQL standard, but I think this feature is very useful as window is very important for pattern detection.
It assumes that there is a system column that defines the timestamp. Only possible in streaming queries, and even then, probably not well defined.
Yes, that's right. For cases where there is no timestamp column, users don't need to define this clause and so there is no side effect.
We should use the SQL standard notation for intervals: WITHIN INTERVAL '3' SECONDS rather than within 3000 milliseconds
Make sense to me.