If your ISP is also hosting your equipment, be sure you know what your access rights are. Incremental backups of customer data are usually done nightly, with a full backup taken about once a week and stored off site. Restores from backup tapes usually take about 48 hours. Usually, the servers can be up and running during backups, though they may take a slight performance hit. Therefore, backups are generally scheduled for the middle of the night.
Backup integrity is a procedure that verifies the backup and restore process actually works.
If this is successful, you can be sure your regularly scheduled backups will do what you expect should the worst happen. A major data loss is the wrong time to find out your backup process isn't grabbing all the necessary files, or the restore isn't able to push the correct files back out. Backup integrity is usually verified about once a month, which is frequent enough to be safe, but not so frequent as to waste staff time. It is extremely important that both you and the ISP are clear on the line of demarcation. This eliminates the possibility of critical functions falling into the cracks, and avoids finger-pointing should something fail.