When I did the big site from classic.
Took 5 days I could not resist to just peek at different things.
But every time I did the import would crash.
Also it does get boring just staring at the screen but it will show errors during the import.
Unfortunately there is not a log to go back and check what happened.
do note, the ubb.threads board was not looked at while the importer was running...at all. the only thing I had loaded in chrome was the actual importer script and phpmyadmin to check on the progress of the importer from the database side of things.