Further to this I have included the code required to build a view using the Day,Hr,Min formula. And for smartness

puts in the Colons.
SELECT FirstDate, SecondDate, CONVERT(Varchar, DATEDIFF(hh, FirstDate, SecondDate) / 24) + ':' + CONVERT(Varchar, 0 - (DATEDIFF(hh, FirstDate, SecondDate) / 24 * 24 - DATEDIFF(hh, FirstDate,
SecondDate))) + ':' + CONVERT(Varchar, 0 - (DATEDIFF(minute, FirstDate, SecondDate) / 60 * 60 - DATEDIFF(minute, FirstDate, SecondDate))) AS NoDaysHrsMins
FROM Database.Table
As you can guess just change the tablename to your table & replace the FirstDate,SecondDate with your date fields.
Messy but I can see no other way of doing this.