It is "up to two years", naturally, as mentioned in the article. I do agree two years is a span that is most likely rarely achieved, but I also remember that a single dose can basically cure* people of PTSD, so I do believe some people might be free of depression for 24 months if they processed their trauma / issues in a significant manner.

Please remember, studies that use psychedelics don't simply hand psychoactive substances to people and send them away, they do receive assistance (e. g. therapy) to process whatever issue they might have.

• again, along with therapy