You're right. The ENSO (El Niño Southern Oscillation) cycle can take up to 7 years, but that's the entire cycle (El Niño, La Niña, and neutral). El Niño conditions may only last months. La Niña typically lasts longer.
This year, they expect El Niño conditions to continue at least til the end of the year.
Also, this past La Niña was unusually long, about three years long. I'm not sure what that signifies but it seems like it might be important.

From climate.gov:

edit: formatting