Great point. I think Fried's example is a little confusing to us because we don't remember right now what days Oct 21 and 22 were. But in the context of the interaction it should be fairly clear that, "Oh, it's just after midnight, Siri's confused because I actually meant today not tomorrow." The actual dates (21 vs 22) wouldn't matter, the two days Siri is trying to choose between is obvious in the moment.
I think the best would have been learning your tomorrow/today pattern and monitoring your use of the phone. For example, a "common" person will continue to use to tomorrow post-midnight until they have slept. The phone should monitor for lack of movement and use over 4-6 hours to identify a sleep schedule that is the person's day divider (patent pending!).