... Upon its release, "Like a Rolling Stone" quickly stood out given its unusually long length of 6:13. In those days, songs played on the radio were usually around three minutes long, as the New York Times noted in 2004. ...
Yeah, back in the day when "Like a Rolling Stone" was released, most radios were AM only.
Car radios were not required to receive FM until the 1970's.
When Did FM Radio First Become Available in Cars?
earthrepairradio.com
Was there ever such a AM/FM mandate for non-vehicle radios, i.e., those in homes?
I cannot find one.
There was the non-duplication rule, though ...
FM Non-Duplication Rule
en.wikipedia.org
... The FM Non-Duplication Rule was adopted by the U.S. Federal Communications Commission (FCC) on July 1, 1964, after a year's consideration.
It limited holders of FM licenses in cities of more than 100,000 who also held AM licenses to simulcasting no more than 50 percent of their AM signal on the FM station.
The commissioners considered the excessive simulcasting wasteful and an impediment to the development of FM broadcasting.
A year later, the FCC reaffirmed the rule, and, after a delay requested by broadcasters, set its effective date for October 1965; some stations were granted exemptions if they could demonstrate their simulcasting served the public good. ...
As I was growing up, we always had an AM/FM radio in the house. I remember listening to WABC in NYC on their FM channel, 95.5.
That non-duplication rule, though, gave rise to FM stations that would broadcast songs longer than the three minute limit of the AM stations.
Can you say WNEW-FM (102.7)? I knew you could.
Let's see the putrid orange chomo match this.
www.911memorial.org