Hi, just modify your code like following,
dataTbl = new DataTable();
DALWorktime dalWorktime = new DALWorktime();
dataTbl = dalWorktime.GetWorkTime();
string StartTime = dataTbl.Rows[0][1].ToString().Trim();
string[] HourAndMinute = StartTime.Split(':');
int Hour = Convert.ToInt32(HourAndMinute[0]);
int Minute = Convert.ToInt32(HourAndMinute[1]);
int Seconds = 0;
int Year = DateTime.Now.Year;
int Month = DateTime.Now.Month;
int Day = DateTime.Now.Day;
DateTime dt1 = new DateTime(Year, Month, Day, Hour, Minute, Seconds);
MainWT_dtpicker_startDay1.Value = dt1;