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Actually, it was Air Time. Ash was actually taking part in a radio story at Goldenrod's Radio Tower, in which he was a prince. Team Rocket pretended to be his character's parents, the king and queen. Then, the all went through a portal to the distant future (radio story-wise).
Sunflora nailed it right on the head. There has been parent imposting by the Rockets (Pokemon Scent-Sation) before but not time traveling to the future.
I'd say this is covered. I'll leave this open for the day in case anyone else wants to chime in and then lock it tomorrow.