Source: Based on historic American Airlines and TWA timetables.
In the 1930s, a flight between New York and Los Angeles would take more than 25 hours, taking about 15 technical stops (range and refueling) and a requirement to change planes twice. Introduced in 1946, the Douglas DC-3 was the first airliner able to undertake the profitable transportation of passengers. It was the outcome of specifications laid down by American Airlines for an airliner that could offer coast-to-coast “sleeper” overnight services. When configured for such operations the aircraft had a capacity of 14 passengers; but in a normal seating configuration, it held 21.
As the above map indicates, the DC-3 with an operating speed of 350 km/hr could cross the continent in about 15 hours, with three refueling stops along the way. TWA (Trans World Airlines) was also competing with the AA “Mercury” services with its own “Sky Chef” route, which was slightly shorter. The eastbound service was organized as an overnight transcontinental crossing so that passengers could arrive on the morning of the next day. The westbound Mercury flight would leave New York at 5:10 PM and arrive in Los Angeles at 7:51 AM.