Hi Martin,
While performing a Unicode Conversion, during Export, Unistall and Import of Database, I would like to improve times for Database Creation since its 5TB
Why don't you drop the entire target system and install from fresh using system copy method.
This will require a parallel system to be setup where you can have target system installed a Unicode system using system copy option.
To minimize the downtime, you may perform parallel Database export import with table splitting.
Regards,
Deepak Kori