The Time Machine is visible in the 6x01 opening (set in 2010) and in a scene in 6x02 (set in 2004). The symbolism behind this is that it took Jimmy 6 years to read an 84 page book
"we need more mentally ill characters!"
*character displays signs of being seriously mentally unwell in a way that isn't romanticizable or cute*
"why are they so mean / evil???"