Hi Paul,
It's reasonable to require information providers to provide consistent UniqueIDs for (choosing a duration out of the thin air) an hour. Supporting constant UniqueIDs for longer periods would be better, with the expectation being that (for a production system) LocalIDs remain constant for many (many) days.
(Stating the same idea, but without choosing a random number: an object's UniqueID value should remain constant for a period far greater than the latency of the underlying information system under normal operating conditions.)
The requirement is much stronger for some of the UniqueID values. For example, a site's CE/SE UniqueID values may be used in CS2SS/SS2CS records published by different sites, so the one site should not change its CE/SE UniqueID values on a whim...