At 19:46 tin the English subtitles on the DVD, Arthur says "You're not serious are you?" but the subtitles have "You're not serious young are you?".
Merlin says he's sending Arthur to somebody who can stop him, and sends Arthur back in time to face Hercules, but it's already been established (in the questionable "making of the TV show" gag episodes) that Hercules remains immortal and still lives even in at the close of the 20th century AD. So there was no need to send Arthur back in time but rather just to another spot on he globe where Hercules is located.