How to find the difference between two time fields in a database table

A proper MS Access query should look like:

SELECT DateDiff ("d", t1.FirstDateTimeField, t1.SecondDateTimeField)
FROM table1 AS t1

See:
DateDiff Function[^]
MS Access: DateDiff Function[^]

You can achieve the same by using vb.net DateFiff function[^], but i do not recommend to use it. Rather than it, use TimeSpan[^]:

Dim departure As DateTime = #06/12/2010 6:32PM#
Dim arrival As DateTime = #06/13/2010 10:47PM#
Dim travelTime As TimeSpan = arrival - departure
Console.WriteLine("{0} - {1} = {2}", arrival, departure, travelTime)
' The example displays the following output:
'       6/13/2010 10:47:00 PM - 6/12/2010 6:32:00 PM = 1.04:15:00