From LedHed's Wiki
Force (near) Instant Replication
- Open AD Sites and Services
- Select a IP Site Link (Under Inter-Site Transports)
- Right Click -> Properties -> Attribute Editor
- Change 'options' attribute to 1 (USE_NOTIFY)
This will cause replication across this site link to happen almost immediately (Like when DC's are in the same site, approximately 15 sec). Essentially when a DC receives a change, it broadcasts a change notification to the other DC, which then replicates the changes as soon as the notification is received.
Only for fast / low latency site links!
References
http://www.mdmarra.com/2013/07/making-active-directory-replication.html