The westbound 20th Century Limited (NYC #25) departed from New York's Grand Central Terminal at 6:00 PM, and arrived at Chicago's LaSalle Street Station at 9:00 AM the following morning. For several years, the arrival time moved forward to 8:45 AM. Also, for several years, the train did not operate on Saturday nights. (For the most part, LaSalle Street Station is still in use in Chicago, serving Metra's former Rock Island commuter services. However, this station is just a shadow of its former self.)
The eastbound (NYC #26) always arrived in New York at 9:30 AM. Departure from Chicago varied ... 4:40, 4:45 or 5:00 PM. Again ... for several years, did not operate on Saturday nights.
Stops included Croton-Harmon (engine change from electric to diesel) and Englewood (suburban Chicago). Other passenger stops were added in later years ... Albany, Syracuse (westbound only), Toledo, Elkhart and South Bend, with Buffalo and Cleveland (not CUT but along the lake) as service/crew stops.
The train carried an RPO car up until shortly before the very end. The train was all-Pullman (sleeping cars) until 1958, at which point a few coaches and sleepercoaches, along with a coach-grill diner, were added to the consist. A twin-unit diner was part of the consist up until the end. However, the separate (full) lounge car (with barber and train secretary) was removed and the kitchen-dormitory car was changed over to a kitchen-lounge when the coaches were added. Always carried the sleeper-observation lounge as its trademark up to the end. The train never carried checked baggage.
For the last month of its life, the Century was combined with the New England States (from Boston - NYC #27 & #28) at Buffalo. #25 times were now 6:00 PM out of NYGCT and 9:40 AM into Chicago; #26 departed Chicago at 4:45 PM, arriving in NYGCT at 10:20 AM.