Songfacts®:

• Guitarist Mick Jones joked in the Westway to the World documentary that "48 Hours" only took about 24 minutes to write. This was obviously a tongue-in-cheek comment, but it is true that a lot of songs on their debut album were written very quickly, and judging by the simplicity of the song's structure, it's probably the case that it was written very quickly.
• The "48 Hours" in the title refers to the 48 hours of the weekend (Saturday and Sunday), and describes the feeling amongst many young people of desperation to have as much fun as possible in the short space of time before Monday and the working week comes around again - or as it's described in the song, the "Jail on Wheels."
  
  Lyrically, it's possible that Joe Strummer was taking inspiration from the 1966 song "Friday On My Mind" by the Easybeats, which he covered many times in the 101ers, the band he was in before he joined The Clash.
• "48 Hours" was quite an inspirational song in the Punk community - the popular punk fanzine 48 Thrills took its name from the chorus lyrics of this song, unsurprising seeing as the editor Adrian Thrills toured extensively with The Clash throughout 1977. He would later take it professional and turn it into a weekly column in the NME magazine. The song also inspired the Jam's "Here Comes The Weekend" and Sham 69's "Hurry Up Harry (Come On)."