This configuration parameter controls how long a domain controller that has failed is considered less preferable to the other domain controllers in the forest that either have not failed or have failed farther back in time.
The default setting is 3600 seconds (one hour).
This parameter helps you avoid domain controllers that appear to be alive, but when they are selected exhibit higher level failures such as crashed, tombstoned, or dead netlogon service.
The value specifies the number of seconds. For example, the following specifies two hours: