Was it possible to fly commercially non-stop from New York City to Los Angeles in 1950; and, if so, what airline(s) offered the service and how long did the flight take?

The Boeing B377 Stratocruiser had a range of 4200 miles, so it was capable of flying non-stop from New York to Los Angeles, a distance of 2440 miles.
The Boeing 377 had a maximum airspeed of 375 mph, so it would have taken around 7 hours.
Pan American had Stratocruisers in their fleet by 1950.
Pan American was doing cross-Atlantic flights by 1950, so it is possible they also had cross country flights.

https://en.wikipedia.org/wiki/Boeing_377
http://www.airwaysmuseum.com/Pan%20Am%20Strat%20at%20EN.htm

United Airlines were operating nonstop flights LA to NY (and SF to NY) in 1954. Flight time was 7 hrs 15 min eastbound and 7 hrs 55 min westbound.

http://file.vintageadbrowser.com/l-pv6xpgbdte1n9v.jpg
http://www.vintageadbrowser.com/airlines-and-aircraft-ads-1950s/2

The website has 112 pages of airline ads from the 1950s.