The expiry period should definitely be configurable, not hard-coded into the software.

I am afraid this request is a waste of time, and can even backfire.

It does not address a serious issue; it is intended as a workaround for situation that in some cases may be a bit confusing and occasionally leads to help requests. But it is highly doubtful if it reduces confusion at all: It adds another layer of complexity, even more so if, as OdMishehu suggests, it would be configurable. In my experience, such added complexity usually widens the variance of user experience, which increases the number of people who will seek help at the Help Desk. That situation is not caused by Wikimedia; it is germane to dynamic IP addresses. It can not be our task to create workarounds for every confusing detail aspect of dynamic IP addresses; we already have one great workaround, which is user registration.