You were talking about distance and now talk about years.
Yes, that expression is used while talking of very great distances. The sun is far away but it takes its light only 8 minutes and 18 seconds. That is a mean distance of 1.496×108 km from Earth. When we say the star in Orion is 800 light years away it means that the light that started from that star 800 years back has reached us only now!
So much for what we see and what the truth is. But to say that the star exists is an illusion but that is generally accepted as true. Similarly that this universe exists is generally true but not really. It is an illusion.
Suppose you are handed over a paper with something written on it in pencil. What do you see? If you see the paper you are ok. If you see the words only then something is wrong.
See the pot here? What was it before? It was mud. What will happen once it breaks? It will be thrown away and mix with mud. It might again become a pot later. Mud always existed, exists and will exist. For a while it had a particular shape and name and was called pot. That did not last long.
The one who sees the pot does not see pot before its creation or after its destruction. But a person seeing the mud sees the mud before the pot was made, while the pot existed and after the pot breaks too. He would be called a viveki.
This world as we see is constantly changing. It exists now but tomorrow it won’t exist as it is now. It would have changed. That is why it is called anitya or ephemeral.