When to delete neighbors?

Two weeks.

I usually just hide them. Once I have other people to replace with, then I will drop them. Many times I have had neighbors that will come back and play after a few weeks off.

If a neighbor goes 5-7 days without clearing their buildings I usually remove that neighbor from my list. I only ever keep 10-15 neighbors on my list so I don't have the numbers to absorb stragglers and part-time players. If they're a long-time dependable neighbor I'll most likely give them more leeway.

Since these events require logging in every 4 hours, I'll usually generously allow up to SIX hours of inactivity before I delete a neighbor.

More then an hour without playing and they're history. Everyone on my list must be just as insane as I am

February 29 you can delete with impunity.

From my point of view, people tend to over-think this issue. It’s not as though you have some moral obligation you need to fulfill or you’ve entered into a binding contract of some sort. If you want to delete ’em, just delete ’em. You don’t need anyone’s permission, nor is there some highly specific definition that definitively tells you when it’s okay to jettison someone.

^ True, it's not difficult to find more friends if needed.

Question: Why hide neighbors? For what reason? You're not doing them any good by hiding them. Why not just delete them?

Yeah I just delete em too. I don't have a specific timeframe, though. I clean up during events like this when I run out of things to tap during visits.