Why does it take a long time to gather design information for certain databases.
It depends on the size of the database and the way the database is designed. If you choose to scan for field values not in the design and you have many views this can take quite a while. Once done however the design is cached and ExportWiz does not have to be scan the whole database again.
If the database design changes in the future you just need to choose refresh design cache for that database under database options when that database is selected.