Watch the episode when Trunks leaves and Piccolo starts to tell the story of what's going to happen in the future!! Piccolo will say"on May 12, at 10:00 AM...." then Goku cuts him off and starts to explain it! Then before they leave Goku says"OK see you guys here on May 12 at 9:00 AM." That's the mistake!!! Watch it and you'll see