What happens to timer in standby mode?

Question

I'm using Timer from Timers namespace. What happens to timer when PC goes to sleep or hibernates?

I have timer set to 6 hours delay.

What will happen in those situations.

1) Timer starts at hour 0 and goes to sleep/hibernation immediately. Then PC wakes at hour 5. Will my timer fire after next 1 hour or after next 6 hours?

2) Timer starts at hour 0 and goes to sleep/hibernation immediately. Then PC wakes at hour 7. Will my timer fire as soon as PC wakes or will it "miss" that one time and fire in next 5 hours? Will it start counting till next event from time of PC waking or from previous "missed" event?

This is something you can easily test for yourself. Try it and post an answer. — Hans Passant, Feb 11 '13 at 22:07
What were the the results when you tried with ,say, 5 mins. Or you haven't tried yet? — I4V, Feb 11 '13 at 22:08
@HansPassant I told at the begging of my question that I'm not able to test it now. — Hooch, Feb 11 '13 at 22:08
Possibly duplicate of http://stackoverflow.com/questions/8229916/how-system-timers-timer-behave-in-wpf-application-after-hibernate-and-sleep — robert4, Jul 01 '16 at 05:09
This is a valid question - especially as reference information. I don't see a reason why it should be closed. IMHO we should rather reopen it. This would also potentially allow more concise answers. — oberlies, May 04 '20 at 07:06

score 28 · Accepted Answer · edited Jul 28 '20 at 16:46

Ok. I asked my friend and this are his results:

23:21:32 : Timer started
23:21:35 : PC Goes Sleep
23:22:50 : PC Wakes
23:22:50 : Timer fired
23:23:50 : Timer fired

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace Test
{
    class Program
    {
        static System.Timers.Timer timer;

        static void Main(string[] args)
        {
            timer = new System.Timers.Timer();
            timer.Interval = 60 * 1000;
            timer.AutoReset = true;
            timer.Elapsed += timer_Elapsed;
            timer.Enabled = true;

            Console.WriteLine(String.Format("{0}:{1}:{2} : Timer started", DateTime.Now.ToLocalTime().Hour, DateTime.Now.ToLocalTime().Minute, DateTime.Now.ToLocalTime().Second));

            timer.Start();

            Thread.Sleep(Timeout.Infinite);
        }

        static void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            Console.WriteLine(String.Format("{0}:{1}:{2} : Timer fired", DateTime.Now.ToLocalTime().Hour, DateTime.Now.ToLocalTime().Minute, DateTime.Now.ToLocalTime().Second));
        }
    }
}

So in short. After sleeping and waking timer checks if it has missed any event. If it missed one it will fire start counting till next event from 0.

@I4V why -1?? This is a good question, and Hooch checked it himself because nobody knows the correct answer. Great! He saved my time) — Mikhail Shcherbakov, Aug 28 '17 at 16:38

What happens to timer in standby mode?

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