As late as possible in the 1990s so that '97 can occur. Also, X-Men '92: House of XCII #1-5 is a previous timeline to either Earth-92131 or Earth-15730. Probably Earth-15730 for consistency since it's literally called the '92niverse.
Essentially, Jubilee has some reincarnation powers and each time she dies, she retains memories of the previous timeline. At the end of the story, she dies but loses her ability to reincarnate, thus forgetting the previous timelines. She's seen in an arcade playing an X-Men game, like the start of the show.