From: "Rich Gauszka" 

'KMS clients renew every seven days by default'

http://www.microsoft.com/technet/windowsvista/plan/faq.mspx

Q. How are KMS activations aged?

A. When a computer activates using a KMS, its client machine ID (CMID) is
added to the n-cache. When the same client renews its activation, the
cached CMID and date stamp are removed and the new activation creates a new
cache entry. KMS clients renew every seven days by default. However, if the
client computer does not renew its activation after 30 days, its CMID is
removed from the n-cache and the n-count reduces by one. To prevent KMS
activation aging from bringing n-count below 25, the KMS caches the CMIDs
of the most recent 50 activations.



Q. What causes KMS-activated computers to go in to RFM?

A. KMS-activated computers enter RFM under any one of the following conditions:

. If they fail to activate within 30 days of installation

. If they fail to renew activation within 210 (180 days plus 30 days grace
period) days of previous renewal

. If they fail to renew activation within 30 days of hard drive replacement

--- BBBS/NT v4.01 Flag-5