If you want it in the form hh:mm, place this in your query:
Tm: Tim(DateDiff("n",[Begin Time],[End Time])/60)
and create a function:
Function Tim(DecTime As Single) As String
Dim hours, minutes As Integer
Dim Min$
hours = Str(Int(Val(DecTime)))
minutes = Str((Val(DecTime) - hours) * 60)
If minutes > 0 Then
If minutes > 10 Then
Min$ = ":" + Right(Str(Int(minutes)), 2)
Else
Min$ = ":0" + Right(Str(Int(minutes)), 1)
End If
Else
Min$ = ":00"
End If
Tim = hours + Min$
End Function
If you just want minutes place this in the query:
Tm: (DateDiff("n",[Begin Time],[End Time])/60)