Hi Lakshimi,
try this function in vb.net
ex: DateAdd(DateInterval.Hour, 12, CDate("1/1/2015 8:00 AM")) 'to add 12 hours from datetime
result: 1/1/2015 8:00 PM
DateDiff(DateInterval.Hour,yourstartdatetime,yourenddate) 'to check difference of two datetime
ex: DateDiff(DateInterval.Hour, CDate("1/1/2015 8:00 AM"), CDate("1/1/2015 2:00 PM"))
result: 6
Jim