DateTime is gong wrong..

Right now i've got a DateTime and i fill it with a date:

DateTime van = dtVan.SelectedDate;
string vanHour = txtTimeFrom.Text.Substring(0, 2);
string vanMin = txtTimeFrom.Text.Substring(3, 2);
int intVanHour = int.Parse(vanHour);
int intVanMin = int.Parse(vanMin);
van = van.AddHours(double.Parse(intVanHour.ToString() + ".00"));

The datetime is in the beginning: {1-10-2008 0:00:00} 

At the end i try to add 15 to it.
But the result is that he goes to: (2-12-2008 12:00:00}

Maybe someone else can help me ?
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