You can set the 'Synchronization Interval' on the directory configuration screen. The synchronization interval is the period of time to wait between requests for updates from the directory server.
The length you choose for your synchronization interval depends on:
If you synchronize more frequently, then your data will be more up to date. The downside of synchronizing more frequently is that you may overload your server with requests.
If you are not sure what to do, we recommend that you start with an interval of 60 minutes (this is the default setting) and reduce the value incrementally. You will need to experiment with your setup.