Hi @sangasangasanga,
use below code
(DateTime.ParseExact("12/30/1899 18:00:00", "MM/dd/yyyy HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture)-DateTime.ParseExact("12/30/1899 08:30:00", "MM/dd/yyyy HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture)).TotalHours.ToString()
Regards,
Arivu