There's nothing to do pre-security at ORD Terminal 5.

Check out of the hotel in late morning, have the hotel store your bags in the bell closet, take the Blue Line into Chicago and hit the Art Institute or the Museum of Contemporary Art, or take the riverboat architecture tour. Have a late lunch. Return to the hotel around 500p or 530p and get your bags out of storage, then get the shuttle to take you over to Terminal 5, arriving around 700p.

If you're at the O'Hare Hilton the Blue Line terminus is right downstairs. If you're at one of the many hotels on the airport periphery, a shuttle will take you to the Rosemont stop (last before O'Hare).