时间格式HH：mm

时间类型转换成其它格式

 string filename = DateTime.Now.ToString("yyyyMMddHHmmss")

时间类型转换成HH:mm

DateTime dt = new DateTime();
dt = DateTime.Parse(data.Tables[0].Rows[j][4].ToString());
 tempSheet.Cells[j + 2, 5] = dt.ToString("HH:mm");

数值秒转换成HH:mm

 int seconds = int.Parse(data.Tables[0].Rows[j][5].ToString());
string  time = string.Format("{00:00}:{01:00}", seconds / 3600, seconds % 3600 / 60);