Is there a wiki on backup settings?

[IriDium]

Xbian provides (almost) all that you desire.

In XBMC Xbian-config -> Backup. Options are given as to the frequency of snapshots. Weekly daily etc.... and the number.

However, it does not specify a time but is triggered by updates. Nor does it request a volume.

So all you really need to do is create a cron job to copy the snapshots to you NAS as and when.

However, I think, this could be an enhancement - to backup snapshots to a specified device.