Understanding ZxBackup restore timespan

Hello guys,
I'm now testing the 30-days trial of Zbackup 1.8.8 on Zimbra open 8.0.4, server is Ubuntu LTS 12.0.4.xx.
I'm using as Zbackup repoository an NFS mounted dir on a Synology NAS, the initializazion threw an error about the dir beeing not case sensitive, but I made tests and it's a false alarm (I can have two dirs like backup and Backup).
I made the mandatory full scan and after that I tried to restore an emal I deleted with the exact time and date and it failed (no emails undeleted).
Then I left the dates as they are presented by the interface and I got 600 undeleted emails with many emails from months ago.
What am I doing worng?
Thanks

Bittone