HI
1. which version of SQL SERVER do you use ? in SQL SERVER 2008 R2 there is time type which can store timespan, there is datetime and datetime2 for store date and time
but no matter if you cannot use the time type you can store your time in the datetime type field and then when you retrive this value from your database you take only the time part and work with
Dim objDate As DateTime = CDate( datarow("DateTimeField"))
Dim objTime As String = objDate.ToShortTimeString()
2. for calculate the difference between two time field you can use TimeSpan or DateDiff like this
Dim timeDiff As Long = DateDiff(DateInterval.Hour, objDate1, objDate2)
or
Dim objDate1 As DateTime = Date.Now()
Threading.Thread.Sleep(3000)
Dim objDate2 As DateTime = Date.Now()
Dim span As TimeSpan = objDate2 - objDate1
Console.WriteLine(span.TotalSeconds)