How busy is o'hare airport at 5:00am ?

for 5:00 AM, my guess is that it will be around a 2 or 3, depending on which airline you are flying, because if you are flying United, there will be people. If you are flying a much smaller airline, and you are in an odd part of the airport you could be there with only the people on your plane. The answer before is very true. O'hare at 5:00PM is KILLER!!! Although, my rule of thumb is to avoid O'hare at all costs, because they cancel and delay flights like no other airport, and they are all pansies when it comes to weather that might "be a problem". Aside from my rant, you will have a good time not being mobbed by people, i just hope your flight still takes off!! Safe travels!