How much time to keep between flights

[scarlet]

Hi

My parents are reaching chicago at 4 pm. then they have to take a connection to madison. how much time do they need at customs and to find gate ? would 2 hours be enough and shall i book the domestic flight at 6 pm?

Thanks

[immihelp]

Better to have at least 3 hours. You never know how much rush may be at O'Hare.