Because public folder replication is e-mail-based, the amount of time it takes for messages to replicate from one information store to a particular replica depends on the underlying messaging system and topology, as well as on administrator-specified MTA connection parameters.
Scheduling for replication is configured in the Administrator program on a per-folder and per-information-store basis. The Replication Schedule property page permits replication scheduling in 15-minute intervals. The same property page exists for the public information store object. If a schedule is set at the folder level, it overrides the schedule set at the information store level.