It was a link between rock and classic music. I will mention also one band named Moody Blues, this band's first seven albums, especially the first, sixth and seventh (sojourn).
We will not forget King Crimson and many others.
Music time signature variation entered at some point, quite soon, it in-itself, into which the collapse many, such as Beggars Opera.
I do not know what were on it first dates, when were we heard it the musical time signature changes. Was is a psychedelic rock song White Room by British music group Cream, in 1998? fine, (while the lyric was in nonsense).