It’s hard to say for sure how much build up one needs to the return of Apocalypse, but the answer according to Marvel editorial in 1999 was … More.
Cable visits X-Force, who are playing video games, to warn them about The Twelve and Apocalypse and how he’s prophecized to die in the battle and all that.
The main story has Caliban returning as the horseman Pestilence and fighting with Cable and X-Force. Rob Liefeld draws #73, but then he needs a rest so Bernard Chang takes over. (I guess Liefeld is just drawing every other issue?)
Caliban is joined by Deathbird, who is the new War Horseman, and together they capture Cable–who is the first of the Twelve that Apocalypse needs for his big return.
I am calling this the start of the Twelve event, since Cable is captured and represents #1 of 12. I mean, there’s been build-up for at least six months now–something has to kick off this event.