add note on difference between CH bucket and own bucket

Author: Blargian

docs/cloud/guides/backups/01_review-and-restore-backups.md

@@ -162,10 +162,14 @@ Backup and restore durations depend on several factors such as the size of the d
 Incremental backups will usually complete much faster than a full backup as less data is being backed up.
 Restoring from an incremental backup will be slightly slower than restoring from a full backup as all incremental backups and the last full backup in the chain are included in the restore as explained above.
 
-In our testing, we have seen that smaller backups ~1 TB could take up to 10-15 minutes or longer to back up.
+In our testing, we have seen that smaller backups of ~1 TB could take around 10-15 minutes or longer to back up.
 Backups less than 20 TB should complete within an hour, and backing up 50 TB of data should take about 2-3 hours.
 Backups get economies of scale at larger sizes, and we have seen backups of up to 1 PB for some internal services complete in about 10 hours.
 
+:::note
+Backups to external buckets may be slower than backups to ClickHouse buckets
+:::
+
 Restore durations are about the same as the backup durations.
 
 We recommend testing with your own database or sample data to get better estimates as the actual duration depends on several factors as outlined above.