using System;

​

public class Program

{

    public static void Main()

    {

​

        TimeSpan interval = TimeSpan.FromHours(6);

        //TimeSpan interval = TimeSpan.FromMinutes(5);

        DateTime dt = DateTime.Now;

        DateTime nextUpdate = RoundTime(dt, interval);

​

        Console.WriteLine("Now : " + dt.ToString("HH:mm:ss.fff"));

        Console.WriteLine("Next: " + nextUpdate.ToString("HH:mm:ss.fff"));      

    }

​

    private static DateTime RoundTime(DateTime baseTime, TimeSpan interval)

    {

        // http://stackoverflow.com/questions/11364481/datetime-round-up-and-down

        var overflow = baseTime.Ticks % interval.Ticks;

        return overflow == 0 ? baseTime : baseTime.AddTicks(interval.Ticks - overflow);

    }

}