To be clear, these were not print advertisements for radio, these were advertisements within FM radio broadcasts. Edwin Armstrong patented Fm broadcasting in 1933 and built the first full-scale FM station himself in 1939. Advertising came to their frequency band two short years later.
As a watch company some marking agent had the bright idea of co-branding the time signal on a radio station with the name of a watch company. Longines first used the gimmick in February of 1927 on WJZ-AM in New York City. They were so impressed with themselves they were still bragging about it in print advertisements in 1941.
FM radio was new and Longines got to FM radio first. They and the Elgin Watch Co. were already buying time on AM radio but this was a first. On December 9th of 1940 the Longines Watch Company inked a deal with W2XOR to broadcast their "time signals" starting in in January of 1941. The station was owned by the Bamberger Broadcasting Service. Both they and sister station WOR-AM, were based in Newark, NJ. (In 1941 the calls changed to W71NY with a commercial license.)
For the Longines-Wittnaur watch company this was just the beginning. They WNBC-AM. This was in addition to two half hours on CBS on Sundays. The Longines Symphonette continued through 1958 rapidly expanded their marketing investments in radio. The Longines Symphonette variety program debuted on CBS in 1943. They also sponsored an off aviation-themed program in 1946 "The World's Most Honored Flights" hosted by Captain Eddie Rickenbacker. In 1950, Billboard reported that Longines bought five half-hour segments a week on CBS.