Question: How long did it take to write the album "Physical Graffiti"?

Context paragraphs:
Sick Again: "Sick Again" is a song by English rock band Led Zeppelin, from their 1975 album "Physical Graffiti".  It was written by Robert Plant about teenage groupies, or as he called them, the "L.A. Queens", with whom the band were acquainted on their 1973 US Tour.

Boogie with Stu: "Boogie with Stu" is a song by English rock band Led Zeppelin from their 1975 album "Physical Graffiti".

Trampled Under Foot: "Trampled Under Foot" is a song by English rock group Led Zeppelin, featured on their 1975 album "Physical Graffiti".

Metaphysical Graffiti: Metaphysical Graffiti is the fifth studio album by The Dead Milkmen, released by Enigma Records in 1990.  The album title and cover art parody the 1975 album "Physical Graffiti" by Led Zeppelin.  Two tracks ("Do the Brown Nose" and "If You Love Somebody, Set Them on Fire") appeared on "Death Rides a Pale Cow".

Black Country Woman: "Black Country Woman" is the fourteenth song on English rock band Led Zeppelin's 1975 album "Physical Graffiti".  It was originally intended to be part of the "Houses of the Holy" album, which had been released two years earlier.

In the Light: "In the Light" is a song by English rock band Led Zeppelin from their 1975 album "Physical Graffiti".  The song was composed primarily by bassist/keyboardist John Paul Jones on his synthesizer, though lead vocalist Robert Plant and guitarist Jimmy Page also received songwriting credits.  It was based on an earlier song the band had written called "In The Morning".

Kashmir (song): "Kashmir" is a song by the English rock band Led Zeppelin.  Included on their sixth album "Physical Graffiti" (1975), it was written by Jimmy Page and Robert Plant (with contributions from John Bonham) over a period of three years with lyrics dating to 1973.  The song became a concert staple, performed by the band at almost every concert after its release.  The song has been described as one of Led Zeppelin's two most overtly progressive epics.

Physical Graffiti: Physical Graffiti is the sixth studio album by the English rock band Led Zeppelin, released as a double album on 24 February 1975 by their newly founded imprint label Swan Song Records.  The band wrote and recorded eight new songs for the album at Headley Grange, which stretched the total time of the record beyond the typical length of a single LP, so the band decided to make "Physical Graffiti" a double album by including unreleased tracks from earlier recording sessions: one outtake from "Led Zeppelin III," three from "Led Zeppelin IV," and three from "Houses of the Holy", including the unused title track from the latter album.

Down by the Seaside: "Down by the Seaside" is a ballad by English rock band Led Zeppelin from their 1975 album "Physical Graffiti".

Ass (album): Ass is the fourth studio album by British rock band Badfinger, and their last album released on Apple Records.  The opening track, "Apple of My Eye", refers to the band leaving the label to begin its new contract with Warner Bros.  Records.  The cover artwork, showing a donkey chasing a distant carrot, alludes to Badfinger's feelings that they had been misled by Apple over the years.  The cover was painted by Grammy Award-winning artist Peter Corriston, who would later create album covers for Led Zeppelin ("Physical Graffiti") and the Rolling Stones ("Some Girls", "Tattoo You").

Supporting paragraphs: Kashmir (song) Physical Graffiti
Answer: over a period of three years