Here is:
root@ns1:~# crontab -l
8,18,28,38,48,58 * * * * /usr/lib/plesk-9.0/postfix-poplockdb-clean
5,20,35,50 * * * * /opt/psa/admin/sbin/backupmng >/dev/null 2>&1
backupmng is well planed, even if I launch it manually, backup doesn't start.
I don't have to...