Depends on the hardware and OVA template with virtualizes servers (#of CPUs). But 2-3 hours for Publisher and 1.5-2 hours for Subscribers is good estimate.
the one I am installing right now seems to take so long to be installed
the following error has shown up a few minutes ago :
then after a while installation continues :
note: by the time shown up I have been waiting for 2 hours.
Ensure that you have an NTP up and running, if you are using DNS ensure forward and reverse lookups are configured and working on the DNS servers.
Callmanagers dont like network connectivity blips and these connectivity blips seem to error out at the extreme end.
So whatever you have set as your network params ensure you dont have dummy entries.
As Chris mentioned the estimate looks good, however you might want to factor an additional 30 minutes for file download and md5 checksum.