The 1997 El Nino certainly developed very fast. Higher than normal SST anomalies first became apparent in mid-February. The event then peaked around October, and maintained itself throughout the remainder of 1997.

In 2002, the NOAA first reported warming in the Pacific in early January. It went on to announce the official return of El Nino in July of that year. It peaked around early winter.

Going back a few years, the 1982-83 El Nino event began in May 1982, with slight ocean warming off the coast of Peru. It reached a high in December 1982, but inexplicably rose to new strengths in April 1983.

It seems that the stronger the event, the faster it develops.

1982-83 - 11 months from first signs to peak
1997-98 - 9 months from first signs to peak
2002 - 11 months from first signs to peak.

It seems that if El Nino is currently in the developing stages, it would hold it's greatest influence very late this year into 2005. At least that's my opinion. Here's a link to data about warm and cold episodes by season:-

Cold and warm episodes by season