using System;

public class Program

{

    public static void Main()

    {

        DateTime start = new DateTime(2023,10,10,12,15,0);

        DateTime end = new DateTime(2023,10,10,12,30,0);

        if (start.IsInRange(new DateTime(2023,10,10,12,10,0), end)) 

        {

            Console.WriteLine(Math.Abs((int)(new DateTime(2023,10,10,12,10,0) - start).TotalMinutes));

        }

        Console.WriteLine(new DateTime(2023,10,10,12,0,0).IsInRange(start, end) + " || " + start.IsInRange(new DateTime(2023,10,10,12,10,0), end));

    }

}

​

public static class Extensions 

{

    public static bool IsInRange(this DateTime testDate, DateTime startDate, DateTime endDate)

        {

            return testDate >= startDate && testDate < endDate;

        }

}