using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var date = DateTime.Now;

        var d = date.AddMinutes(15);

        var x = new [] {

            date.AddMinutes(1),

            date.AddMinutes(2),

            date.AddMinutes(3),

            date.AddMinutes(4),

            date.AddMinutes(5), //

            date.AddMinutes(6),

            date.AddMinutes(7),

            date.AddMinutes(8),

            date.AddMinutes(9),

            date.AddMinutes(10), //

            date.AddMinutes(11),

            date.AddMinutes(12),

            date.AddMinutes(13),

            date.AddMinutes(14),

            date.AddMinutes(15) //

        };

        var y = x.Where(o => Math.Floor((d - o) / TimeSpan.FromMinutes(5)) == (d - o) / TimeSpan.FromMinutes(5)).ToArray();

        Console.WriteLine(y[0]);

        Console.WriteLine(x[4]);

        Console.WriteLine("======");

        Console.WriteLine(y[1]);

        Console.WriteLine(x[9]);

​

        Console.WriteLine("======");

​

        Console.WriteLine(y[2]);

        Console.WriteLine(x[14]);

    }

}