17. What’s the difference between a site link’s schedule and interval?

Windows admin interview questions (includes Vista)

Any time two networks are separated by links that are heavily used during parts of the day and are idle during other parts of the day, put those networks into separate sites. You can use the ability to schedule replication between sites to prevent replication traffic from competing with other traffic during high usage hours.
In simple words you can define it as the time when you allow the replication to happen.
Interval is also a part of schedule but it takes cares of the replication polling frequency. In other words in a said schedule of say 9:00 AM to 1 PM replication polling shuld occur in every 15 minutes.
Schedule here is 9:00 AM to 1 PM
Interval is every 15 minutes.