Up until when can I get the pre-order ring?

Until when?

For endwalker

It's an earring, not a ring. You can pre-order up until at least the release day, which is the 23rd. Early access begins on the 19th but I think you can still pre-order after that and get half the early access instead, but just in case, you should be thinking to get it before the 19th.

Early access starts on the 19th, so i imagine you need to pre-order by the 18th. I dont think you can pre-order once the early access window opens, though i could be wrong about that.

Preorders during early access are still preorders. You need to buy it before official launch.