After making a change on one Domain Controller, what is the minimum amount of time you should expect for updates to propagate to all DCs?

The correct answer is based on the standard behavior of Active Directory replication. When a change is made to one Domain Controller, it generally takes a minimum of 15 seconds for the change to be replicated to other Domain Controllers within the same site due to the default replication interval. However, the actual time for replication across different sites can be longer, as it can take up to 180 seconds (or more in certain configurations). Since the replication may encounter various network latencies and processing times, it often takes slightly longer than the minimum interval to ensure that the updates propagate successfully to all Domain Controllers.

The choice of 36 seconds reflects a consideration of average scenarios in real-world practices, accounting for network conditions and variations that could influence the speed of replication beyond the minimum timing observed in ideal conditions. Therefore, 36 seconds is a practical expectation when factoring in these possibilities within a controlled environment.