Start DispatcherTimer from N seconds, minutes, hours

Question

I have been searching for information and couldn't find any. My question is how to start DispatcherTimer from N seconds or minutes or hours. I mean currently it starts from 00:00:00 (also displayed in CurrentTime Label) but if I would like to start it from 00:00:30 (also display in CurrentTime Label), what should be differently?

To clarify it more... When I start an application I execute StartWorkingTimeTodayTimer(). Then I have a Label (CurrentTime) that is starting to show time of application runtime. Currently it starts from 00:00:00. I would like to display for example 00:00:30 at Start and then tick by one second as it is right now... so 00:00:30 -> 00:00:31 -> 00:00:32 -> 00:00:33 -> 00:00:34 ->

I have tried to play with:

DateTime x30SecsLater = StartTimeWholeDay.AddSeconds(30);

without success.

Current code:

private static DateTime StartTimeWholeDay;
private DispatcherTimer _dailyTimer;

public void StartWorkingTimeTodayTimer()
{
    StartTimeWholeDay = DateTime.Now;
    DateTime x30SecsLater = StartTimeWholeDay.AddSeconds(30);

    _dailyTimer = new DispatcherTimer(DispatcherPriority.Render);
    _dailyTimer.Interval = TimeSpan.FromSeconds(1);
    _dailyTimer.Tick += (sender, args) =>
    {
        CurrentTime = (DateTime.Now - StartTimeWholeDay).ToString(@"hh\:mm\:ss"); // DateTime.Now.ToLongTimeString()
    };
    _dailyTimer.Start();
} 

---

EDIT:

I have tried already:

public void StartWorkingTimeTodayTimer()
{
    StartTimeWholeDay = DateTime.Now;
    DateTime x30SecsLater = StartTimeWholeDay.AddSeconds(30);

    _dailyTimer = new DispatcherTimer(DispatcherPriority.Render);
    _dailyTimer.Interval = TimeSpan.FromSeconds(1);
    _dailyTimer.Tick += (sender, args) =>
    {
        CurrentTime = (DateTime.Now - x30SecsLater).ToString(@"hh\:mm\:ss"); // DateTime.Now.ToLongTimeString()
    };
    _dailyTimer.Start();
}

but it calculates backwards...

It should go the other way 00:00:30 -> 00:00:31 -> 00:00:32 -> 00:00:33 -> 00:00:34 ->

Answer 1

After struggeling a LONG time to get WPF running with a console (in .NET 5) ...I failed, so I'll give the answer using System.Timers. But you get the idea.

using System;
using System.Timers;

namespace TimerExample
{
    class Program
    {
        private static DateTime _startTime;

        private static void OnTimedEvent(object source, ElapsedEventArgs eea)
        {
            Console.WriteLine((eea.SignalTime - _startTime)
                .Add(TimeSpan.FromSeconds(29)) // 29, because the first trigger happens 1 sec after start
                .ToString(@"hh\:mm\:ss"));
        }

        static void Main(string[] args)
        {
            _startTime = DateTime.Now;
            var timer = new Timer
            {
                Interval = 1000, // msec
                AutoReset = true,
            };
            timer.Elapsed += OnTimedEvent;
            timer.Start();

            Console.WriteLine("Press any key to stop");
            Console.ReadKey();
        }
    }
}

OR

using System;
using System.Timers;

namespace TimerExample
{
    class Program
    {
        private static DateTime _startTime;

        private static void OnTimedEvent(object source, ElapsedEventArgs eea)
        {
            Console.WriteLine((eea.SignalTime - _startTime)
                .ToString(@"hh\:mm\:ss"));
        }

        static void Main(string[] args)
        {
            _startTime = DateTime.Now.AddSeconds(-29); // again 29 instead of 30
            var timer = new Timer
            {
                Interval = 1000, // msec
                AutoReset = true,
            };
            timer.Elapsed += OnTimedEvent;
            timer.Start();

            Console.WriteLine("Press any key to stop");
            Console.ReadKey();
        }
    }
}