There is no need to use the bug forum: "The expansion will be complete in approximately X days", tells you exactly like it is. The expansion will be completed in APPROXIMATELY X days. Sometimes you get lucky and a 8 day build is finished in 6 days, and sometimes you will have bad luck. I started a 7 day build om March 14th, and it still is going to take 2 more days to finish it..
Yes, very rarely you can be lucky as well.
I started an 8 day expansion on March 19th and as of today it is going to take 2 more days - that would be 2 days early.