Export is very Slow with Output Management Web Viewer 12.1. There is a long pause between setting definitions.
The page limit was set very high.
The page limit was set to a very high value, 500 in Administration->Preferences->Display preferences->Number of pages per request.
When it was reset to 10, this made the export much faster and is now acceptable. Users will still be able to search through the whole report - the limit does not affect the find.