It only took about six months to refurb Tokyo's Space Mt. I don't think they replaced a significant amount of track, though.
Thats because Tokyo's was the youngest of the first three space mountains.
Scary thing is Disneyland's Space Mountain was younger Magic Kingdoms and has already gotten its track replaced because it was getting dangerously old and WDW is still clinging onto the original rickety track from the 1970s. If they don't replace that soon there gonna have an accident God Forbid.