Insert Time in Database using C# and VB.Net in ASP.Net

I am facing this issue in asp.net webform from the day one when i started working as a developer .

Anyone suggest me what is the best practise to avoid this error any more please...

i used many different method to deal it but not successfull (Convert.TODatetime,Tryparse ,culcture etc)

   protected void Button1_Click(object sender, EventArgs e)
   {               
       {
           string EmpName = txtname.Text;
           string EmpContact = txtcontact.Text;
           string IDDept = DDDept.SelectedValue;
           string IDSubDept = DDSubDeptID.SelectedValue;
           string IDDesig = DDDesigID.SelectedValue;
           string status = DDStatus.SelectedValue;
           string JoinDate = txtjdate.Text;
           string LeftDate = txtldate.Text;
           string Empcur = DDCur.SelectedValue;
           string Lentitled = CheckBox1.Text;
           string address = txtaddress.Text;
           string OTEntitled = DDOTSt.SelectedValue;
           string PL = txtPL.Text;
           string Dhour = txtdhour.Text;
           string LTime = (txtlTime.Text).ToString();
           string OTRate = txtOTRate.Text;
           //     string namDept = DDDept.SelectedValue;
           string query = "INSERT INTO EmployeeDetails VALUES(@EmpName,@EmpContact,@IDDept,@IDSubDept,@IDDesig,@status,@JoinDate,@LeftDate,@Empcur,@Lentitled,@Address,@OTEntitled,@PL,@Dhour,@LTime,@OTRate) ";
 
           con = new SqlConnection("Data Source=IT;Integrated Security=SSPI;Initial Catalog=AttendanceManagement");
 
 
           using (SqlCommand cmd = new SqlCommand(query))
           {               
               cmd.Parameters.AddWithValue("@LTime", LTime);
               cmd.Parameters.AddWithValue("@OTRate", OTRate);
               if ((txtjdate.Text == ""))
               {
                   cmd.Parameters["@JoinDate"].Value = DBNull.Value;
               }
               else
               {
                   cmd.Parameters["@JoinDate"].Value = DateTime.Parse(txtjdate.Text);
               }
 
               if ((txtldate.Text == ""))
               {
                   cmd.Parameters["@LeftDate"].Value = DBNull.Value;
               }
               else
               {
                   cmd.Parameters["@LeftDate"].Value = DateTime.Parse(txtldate.Text);
               }
               cmd.Connection = con;
               con.Open();
               cmd.ExecuteNonQuery();
               con.Close();
               Response.Redirect(Request.RawUrl);
           }
       }
   }      

Thanks in advance