Did you try to divide by a non integer ?
Try to replace
DATEDIFF(mi, dbo.Trn_Daily3.Dr_TimeStart, dbo.Trn_Daily3.Dr_TimeEnd)/60
with
DATEDIFF(mi, dbo.Trn_Daily3.Dr_TimeStart, dbo.Trn_Daily3.Dr_TimeEnd)/60.0
as for many languages like C, C++, C#
a divide of integers result in an integer.