If you are fully lucid, you are in a conscious mindframe. And in my lucid dreams, when I do become lucid the fact base things of reality are there with me.
So you either claim they don't exist. But if that were the case and time dialation accured, it would not be 500 or 800 years. So you should be able to percieve otherwise.
So I do not see how this is possible.
In all the lucid dreams that I have messed with time, the more lucid I was, the more time was consistant. And visa versa. Which to me would say that the more opaque the lucidity, the more potential there is to percieve time incorrectly.