Ideally, hot backups consist of the latest snapshot with all of the transaction logs applied to the it, except the transaction log currently being written. The system can get behind in applying the transaction logs, depending on how busy the system is. It is possible that there might be several log files that have not yet been applied to either the database or the hot backup.
This “almost duplicate” of the live database is designed to minimize down time and data loss if something catastrophic happens, or if a corruption of the database is detected.
A new hot backup is started every 24 hours when a new snapshot is taken. The old hot backup is verified and kept until purged. For more information, see 9.2.3 How Circular Backups Work in a Calendar Server 6.3 System.