Answer is - it depends on your database

Answer is - it depends on your database structure. You should be processing on average about 2-5mln rows per minute. But distinct count measure groups processing time could be slower. Also, it could be that your relational database is slowing down your processing if you do any calculations/joins during load. Process each measure group or even partition manually (from SQL Server Management Studio) and watch what is happening during processing - for example how much time till you see that records are read, how much time to build index, etc. Then focus on performance tuning for measure groups that are slow...