The minimum time a flight between Chicago and Singapore would take is 19 hrs 15 mins. This assumes a non-stop speed of 500mph, 30 mins for take off and landing, and a flight travelling from from east to west (over the Pacific).
In reality, such flights travel west to east, include stops and so often take much longer. This is also one of the longest routes it is possible to fly.
Flight duration depends on a few things:- Which air carrier you use,
- How many stops are required
- How much you pay for the ticket - the more expensive, the less time the flight takes is a general rule.
The Average Time to Fly from Chicago to Singapore is 28-29 Hours
The shortest flight I found was 23hrs 25mins and is a Delta Airlines flight, changing at Detroit and Seoul.
The longest flight duration was 38hrs 55mins, a KLM flight stopping at Atlanta and London (an overnight stop).
Other popular stopping off points for Chicago - Singapore are Dubai and Hong Kong.
If you're heading for Singapore, here's a clip listing some places to visit when you arrive: