India's a big place so flight times will vary depending upon the exact destination. Additionally, I doubt that there are any direct flights from General Mitchell International to India.
To get to Delhi, it's necessary to change at Chicago O'Hare. Total flight times range from about 17 hours to 20 hours. For more accurate information, enter your destination and travel dates, here: http://www.innovata-llc.com/milwaukee/default. asp