The first thread on replication after Emmanuel's comments started taking a turn towards the question of time synchronization across replicating servers. Time synchronization is very nice to have and forget about while writing the code around replication. And yes we do not have control over it since administrators can fudge this up.
Another alternative would be to have all the servers in the cluster communicate with one another on occasion to share their current time to establish offsets. These offsets (differences in time) between servers in replication agreements can be used to correct for any time variance we might encounter. Furthermore if the time is adjusted on the hosts, the cluster can adjust to time changes.