Hi,
The replication for password change is a Immediate Replication.
When you change a password for users or machines, password changes are sent immediately to the PDC FSMO. The PDC operations master then locally stores this value. And the password change is then replicated to its partners using the Active Directory replication process. Down-level domain controllers replicate the change directly from the PDC FSMO role owner.
For the Active Directory replication inter-sites: it depends on the replication schedule you defined .Site-links, site costs and replication schedules are what we user to control the inter-site replication. It also effected by sites bandwidth, latency and ect.
For the Active Directory replication intra- sites :By default, (according to Microsoft) any domain controller will aware of any directory update within 15 seconds. Within site despite the number of domain controllers, any directory update will be replicate in less than one minute.
Best Regards,