This sub-version of 7.3 installation no longer appears to run as “unattended”, at least for me. When I select that method, it still prompts me to manually set the date, partitioning etc. So there is no difference between unattended and interactive installation methods. I have tried multiple times but getting same results.
My bad. I have realised that this was because the disk was less than the required size. When I did 12GB disk size, the unattended install worked fine.