You can override the default replication interval for intersite links.
To do it, go into adsiedit with an Enterprise Admin account.
Navigate to the siteLink object you want to set change notification for, and edit the options attribute.
The first bit needs to be 1. Generally, the attribute will not be set so just set it to 1. Otherwise you'll need to do a bitwise OR calculation on it to add the 1.
Once this is done, allow the configuration partition change to replicate to all affected DCs in those sites. After it has done, all further changes made to the AD on DCs in those sites will replicate between the 2 sites faster using change notification.