In 2019, it was 14-18 minutes of explicit advertising per hour depending on the network and the genre (https://www.statista.com/statistics/1025656/ad-time-primetim...), up from about 13-16 minutes per hour in 2009 (https://time.com/96303/tv-commercials-increasing/). "Bumpers", network identifiers, and other content inserted by the airing network that is not ad space sold to a third party are not included in all of the counts. Local (as opposed to national) advertising time is also missing from some of these datasets. Overall, the duration of scripted US television shows is now approximately 40 minutes per hour: http://www.waynesthisandthat.com/commerciallength.htm
Other ways television advertising has increased over time:
Number of ad breaks. In the 1950s and early 1960s ads were aired before and after shows, often with the host of the show doing the ad reads for one or two products that were billed as the show's "sponsors". A break for ads in the middle of the content was added in the mid-1960s, and the number of breaks per hour increased at least into the 1990s. https://ibuzzle.com/television-advertising-history
Number of ads per break. Television ads have gotten generally shorter over time. 30 seconds became the norm during the 1970s. From 2009 to 2019, the percentage of ads that were 15 seconds long increased from 35% to 42% (https://time.com/96303/tv-commercials-increasing/).
Other ways television advertising has increased over time:
Number of ad breaks. In the 1950s and early 1960s ads were aired before and after shows, often with the host of the show doing the ad reads for one or two products that were billed as the show's "sponsors". A break for ads in the middle of the content was added in the mid-1960s, and the number of breaks per hour increased at least into the 1990s. https://ibuzzle.com/television-advertising-history
Number of ads per break. Television ads have gotten generally shorter over time. 30 seconds became the norm during the 1970s. From 2009 to 2019, the percentage of ads that were 15 seconds long increased from 35% to 42% (https://time.com/96303/tv-commercials-increasing/).
Amount of paid product placement inside the shows. In 2009, product placement occupied between 5.5 minutes and 19.25 minutes per hour, with unscripted shows the highest (https://www.marketingcharts.com/television-9434). Spending on television product placement has increased since then (https://www.marketingcharts.com/cross-media-and-traditional/...).
Addition of advertising to previously ad-free platforms. I recall that most cable networks originally did not air ads but cannot find the data to back that up. In 2021-2022, streaming services have increasingly added ads: https://www.marketingcharts.com/television/tv-advertising-22... In a 2022 survey, 41% of American TV-watching adults felt there were too many ads on television vs. 18-25% for various streaming platforms (https://hubresearchllc.com/reports/?category=2022&title=2022...).