Run this before running DBCC Shrinkfile/Emptyfile, open a SSMS window:

select getdate()

dbcc showfilestats

This will give you a baseline of how many extents (8 x 8Kb pages) there are in each file storing table data. Total extents correlates to the total file size (# extents x 640Kb). Used extents shows how many extents are actively being used to stored data. DBCC Shrinkfile/Emptyfile will move each extent and spread it to one of the other data files.

As the shrinkfile progresses, the used extent count will fall. Since Shrinkfile/Emptyfile assures you that no new data will be added to the file, you are then waiting for this value to reach zero.

After a period of time, open another SSMS window and run the above command again. Then you can simply calculate the differences of the extents used and the elapsed minutes to get a extents/min rate. Take the number of extents left and divide by the rate and that will give you an accurate estimate of the time remaining.

Hope this helps.