using System;                   

using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        int? udHours = 5;

        int? udMinutes = 10;

        var dateString = String.Format("{0:00}:{1:00}", udHours.Value, udMinutes.Value);

        Console.WriteLine(dateString);

        DateTime remdate = DateTime.ParseExact(dateString, "HH:mm", CultureInfo.InvariantCulture);

        // remdate = remdate.AddDays(1);

        TimeSpan time_span = remdate - DateTime.Now;

        Console.WriteLine(String.Format("{0} nap {1} óra {2} perc {3} másodperc van hátra", time_span.Days, time_span.Hours, time_span.Minutes, time_span.Seconds));

    }

}