[Grammar] The film will end when you finish dinner.

[Son Ho]

Good afternoon, everyone. Could you help me with the two following sentences ( in a workbook)?

EXAMPLE 1: The film will end when you finish dinner.
EXAMPLE 2: By the time the film ends, you will have finished dinner.

In my opinion, the two sentences have the same meaning. They mean the action "you will finish dinner" happens first and then the second one " the film will end" follows. Please explain if I were wrong. Thanks in advance.

 

[Raymott]

1 is not a natural sentence. It's ambiguous. It could mean that the film ending and your finishing dinner occur at the same time. You could imagine that you have finished dinner, but the film hasn't ended yet. That would make 1 wrong. It's just not something we'd say. It seems to imply that you can make the film end by timing the end of your dinner, which doesn't happen.
It would be better to say, "The film will end when you've finished dinner". But again, no one would say that.