SqlDataReader.GetTimeSpan doesn't exist in mono for unity but exists in visual studio help!

Hi everyone, i looked at other answers to see if the question has been submitted before and i couldn't find what i want.

basically i need to get some data which are located in a sql server. I entered data manually in the sql server and by following some tutorials, i am able to connect to the database, enter a sql request and get values. (good)

To store values, i declare variables with the related types and while the SqlDataReader is reading, i store the data in my variables. I am encountering a problem with the TimeSpan type. On visual studio, my C# script is perfectly working and i can get the TimeSpan type value with the following line of code :

 SqlDataReader reader = cmd.ExecuteReader(); 
 TimeSpan time;
 while (reader.Read())
 {
 time = reader.GetTimeSpan(1);
 // and i display it with Debug.Log in unity or Console.WriteLine in VS
 }

This code works on visual studio but when i copy it into a C# script in mono, it doesn't work and i got an error at "reader.GetTimeSpan()" saying "error CS1061: Type `System.Data.SqlClient.SqlDataReader' does not contain a definition for GetTimeSpan and no extension method GetTimeSpan of type System.Data.SqlClient.SqlDataReader could be found (are you missing a using directive or an assembly reference?"

I couldn't find a solution until now because the function does exist in C# and we can find it online on the documentation but not in mono. Because we need to add some .dll into the assets or plugins folder to make it work, i guess the dll for VS must be different but i don't understand why and i don't know which ones i should add to my project . Anyone can help me?

Here is the full script:

 using UnityEngine;
 using System.Collections;
 using System;
 using System.Collections.Generic;
 using System.Data;
 using System.Data.SqlClient;
 using System.Diagnostics;
 using System.Linq;
 using System.Text;
 //using System.Threading.Tasks;
 
 public class GetTime : MonoBehaviour {
 
 
 
     // Use this for initialization
     void Start () {
         getTime ();
     }
     
     static void getTime()
     {
         string connectionString = null;
         SqlConnection conn;
         connectionString = "Data Source='addServerName';User ID='addUserId';Password='addPassword'";
         conn = new SqlConnection(connectionString);
         try
         {
             conn.Open();
         //    Debug.Log("Connection Open ! ");
 
         }
         catch (Exception ex)
         {
             Console.WriteLine("Can not open connection ! ");
         }
 
         SqlCommand cmd = new SqlCommand("SELECT  Heure FROM [myDatabase]", conn);
         SqlDataReader reader = cmd.ExecuteReader();
 
         TimeSpan heure;
         while (reader.Read())
         {
             heure = reader.GetTimeSpan(0);
 
         //    Debug.Log("{0}", heure);
         }
         reader.Close();
         conn.Close();
     }
 }