/var/log/univention/system-setup-boot.log is corrupted, even:
Is there another way how to find out when UCS was installed?
Yes, there is. Get the name of your boot-partition run:
df /boot | grep -Eo '/dev/[^ ]+'
And run this, where name is the result of your previous query:
tune2fs -l /dev/name |grep --color created