Yet more questions about the log pose

I thought I understood how the log pose works, but I've just started the Skypiea arc and am now confused.

Once a log pose calibrates to the island it's currently on, it will then point to the next closest island within the chain of islands the log pose is in, out of the 7 chains that run from Reverse Mountain to Laugh Tale, yes?

When Nami's log pose points to the sky island, she decides to use the Jaya eternal pose Robin stole to find answers on Jaya, with the intent to return to the sky island. Evidently, this means the log pose will continue to point to the sky island, even if they get closer to Jaya? (From Nami's perspective).

Okay, so that means once a log pose binds to the next island, it will forever point to that island, regardless of where the log pose ends up, so long as the log pose doesn't get reset at a different island?

While on Jaya, Nami asks a bartender how long it will take the log pose to reset. The bartender answered "4 days". Nami then whispers to herself, "that means we can't even stay here more than 2 and a half days."

....Why? If the log pose resets after 4, doesn't that mean you have 4 days before it loses its pull toward the sky island?