How to Write Query in C#

Can you pls eloborate on the issue?
You are converting TIME column to Varchar and checking if its value is between string tstr1 and tstr2, which you cannot do.
The better way to do is convert the values of tstr1 and tstr2 into Time(DateTime) values and then check the condition.

To create a project

Start Visual Studio.

On the menu bar, choose File, New, Project.

The New Project dialog box opens.

Expand Installed, expand Templates, expand Visual C#, and then choose Console Application.

In the Name text box, enter a different name or accept the default name, and then choose the OK button.

The new project appears in Solution Explorer.

Notice that your project has a reference to System.Core.dll and a using directive for the System.Linq namespace.

The data source for the queries is a simple list of Student objects. Each Student record has a first name, last name, and an array of integers that represents their test scores in the class. Copy this code into your project. Note the following characteristics:

The Student class consists of auto-implemented properties.

Each student in the list is initialized with an object initializer.

The list itself is initialized with a collection initializer.

This whole data structure will be initialized and instantiated without explicit calls to any constructor or explicit member access. For more information about these new features, see Auto-Implemented Properties (C# Programming Guide) and Object and Collection Initializers (C# Programming Guide).

and write following code

public class Student
{
    public string First { get; set; }
    public string Last { get; set; }
    public int ID { get; set; }
    public List<int> Scores;
}

// Create a data source by using a collection initializer.
static List<Student> students = new List<Student>
{
   new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores= new List<int> {97, 92, 81, 60}},
   new Student {First="Claire", Last="O’Donnell", ID=112, Scores= new List<int> {75, 84, 91, 39}},
   new Student {First="Sven", Last="Mortensen", ID=113, Scores= new List<int> {88, 94, 65, 91}},
   new Student {First="Cesar", Last="Garcia", ID=114, Scores= new List<int> {97, 89, 85, 82}},
   new Student {First="Debra", Last="Garcia", ID=115, Scores= new List<int> {35, 72, 91, 70}},
   new Student {First="Fadi", Last="Fakhouri", ID=116, Scores= new List<int> {99, 86, 90, 94}},
   new Student {First="Hanying", Last="Feng", ID=117, Scores= new List<int> {93, 92, 80, 87}},
   new Student {First="Hugo", Last="Garcia", ID=118, Scores= new List<int> {92, 90, 83, 78}},
   new Student {First="Lance", Last="Tucker", ID=119, Scores= new List<int> {68, 79, 88, 92}},
   new Student {First="Terry", Last="Adams", ID=120, Scores= new List<int> {99, 82, 81, 79}},
   new Student {First="Eugene", Last="Zabokritski", ID=121, Scores= new List<int> {96, 85, 91, 60}},
   new Student {First="Michael", Last="Tucker", ID=122, Scores= new List<int> {94, 92, 91, 91} }
};