No backups have been created for more than 5 day(s)

Is there a way of changing when this emailed alert gets posted, as we do a full system backup every Sunday morning at 1 second past midnight?

I have been to ‘alerts/settings/last successful backup’ and changed ‘Time-Based’ alerts to 8 days.
But still I get the message X 5 for each server.

Warning alert: No backups have been created for more than 5 day(s) Occurred: 04/01/2013 00:18:59
Alert type: Data protection
Machine: Engineering2.peakgroup.com
Description: 'Engineering2.peakgroup.com': No backups have been created for more than 5 day(s).

I don’t want to turn off ‘Data Protection’ alert just extend its days timeout.
Anybody help on this?