See log file. The media is loaded at 11:00 pm when the job is scheduled to start. However the summary shows it did not actualy start backing anything up until 9:52 am the next morning.
Family Name: "Media created 7/3/2006 11:00:04 PM"
Backup of "\\ES001\Microsoft Exchange Mailboxes "
Backup set #1 on storage media #1
Backup set description: "Backup 0005"
Backup Type: DIFFERENTIAL - Back up changed messages
Microsoft Exchange Server Agent: Started
Backup started on 7/4/2006 at 9:25:22 AM.
Backup completed on 7/4/2006 at 10:07:27 AM.
Backup Set Summary
Backed up 5082 mail message(s) in 3070 folder(s) in 79 mailbox(es)
Processed 263,622,820 bytes in 42 minutes and 5 seconds.
Throughput rate: 5.97 MB/min