How does Ra measure Time?

[anagogy]

Why not?

That could be an excellent explanation to Ra can stay with us in any point of time but yet make mistakes.

Because of "probability drift". When you go back in time, you simply go back into another parallel probable version of your past. Another similar, but slightly different refraction, of the infinite light. It would be extremely difficult to find the exact conditions, or probability wave, that gave birth to our present causality stream because you can't unknow what you know and that affects your movement through time. And yes, that could be one reason why Ra can't go back and undo their mistake. But going back to the Meier case, i believe some beings do have the technology to go back to that exact probability stream that gave rise to our probability stream, but I believe it is extremely advanced technology (most beings can't pull off this trick). I think Ra could do it, but they are not "allowed to" because it amounts to an even greater infringement than their original "mistake", though, I don't really consider their foray with the Egyptians a mistake. After-all, as they also stated, there are no mistakes under the Law of One. Just different journeys back to the creator.

Anyway, these are just my personal opinions. Unfortunately I don't have any proof. Just dialogs I have with my own inner teachers, as many here do as well. Feel free to discard if it doesn't rez with you.