using System;

public class Program

{

    public static void Main()

    {

        var limit = 20;

        var maxDelay = 43200;

        var nextExecution = new DateTime(2020, 02, 25);

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

        var delay = 1;

        for (var i=1;i<=limit;i++)

        {

            delay = delay * 2;

            delay = delay > maxDelay ? maxDelay : delay;

            nextExecution = nextExecution.AddSeconds(delay);

            Console.WriteLine("Retry {0} : {1}s delay -> {2:dd/MM/yyyy HH:mm:ss}", i, delay, nextExecution);        

        }

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

        var postingDate = new DateTime(2020, 02, 25); // need to calculate from something which doesn't change

        var retry = 2;

        Console.WriteLine("{0} : {1:dd/MM/yyyy HH:mm:ss}", retry, GetNextExecution(postingDate, retry));

        retry = 5;

        Console.WriteLine("{0} : {1:dd/MM/yyyy HH:mm:ss}", retry, GetNextExecution(postingDate, retry));

        retry = 8;

        Console.WriteLine("{0} : {1:dd/MM/yyyy HH:mm:ss}", retry, GetNextExecution(postingDate, retry));

        retry = 12;

        Console.WriteLine("{0} : {1:dd/MM/yyyy HH:mm:ss}", retry, GetNextExecution(postingDate, retry));

        retry = 25;

        Console.WriteLine("{0} : {1:dd/MM/yyyy HH:mm:ss}", retry, GetNextExecution(postingDate, retry));

    }

    private static DateTime GetNextExecution(DateTime nextExecution, int attempt){

        var delay = 1;

        var maxDelay = 43200;

        var limit = 20;

        if (attempt > limit) {

            return GetNextExecution(nextExecution, limit);

        }

        for (var i=1; i<=attempt; i++)

        {

           delay = delay * 2;

           delay = delay > maxDelay ? maxDelay : delay;

           nextExecution = nextExecution.AddSeconds(delay);

        }

​

        return nextExecution;

    }

}