It's a pun on an existing Scheme implementation, Scheme 48 [1]. This was a research implementation by Jonathan Rees and Richard Kelsey that was so named because it was supposedly written in 48 hours. The idea for the tutorial was that "Hey, anybody can write a Scheme in 48 hours, you don't have to be an accomplished professor!"
48 hours is actually somewhat ambitious - it took me about 3 months of nights & weekends time to write it (although that also included teaching myself enough Haskell to write the implementation all the way through first before writing it up as a tutorial). It's probably technically possible to go through it in a weekend and write yourself a Scheme, but to really learn things in depth may take a bit longer.
48 hours is actually somewhat ambitious - it took me about 3 months of nights & weekends time to write it (although that also included teaching myself enough Haskell to write the implementation all the way through first before writing it up as a tutorial). It's probably technically possible to go through it in a weekend and write yourself a Scheme, but to really learn things in depth may take a bit longer.