As everyone else has already said, by no means expect the Amtrak to be on time, especially if you're coming in from far away.

ORD is not known for reliability either, espeically during rush hour. O'Hare has common delays and getting from there to downtown can take a while during that time of the day.

If you really need to be downtown by 9am, I would strongly consider getting in the night before and having a more peaceful morning.