How to count down on 60 minutes, do something every hour

Question

I want to do something every hour.

It does not need to be very accurate, 1 to 5 seconds is ok.

Can I use a timer with a interval of 3600.000ms?
The proces may not be depend on other process in the computer or the use of the UI.

Currently I use a timer that elapses every 900 ms.

Than I calculate
TimeLeft = TimeSpan.FromHours - (Date.Time.Now - BeginTime);

if (TimeLeft <= TimeSpan.Zero)
{
do something
}

but this calculation fails once a day.

What method would you use ? Timer or calculation, something else.
Why is the calculation failing ?
What can I do to improve this ?

Answer 1

I haven't had problems with longer running timers, in console applications. I would probably just set an interval of 1 hour :)

That is, if this timer is running in the context of a bigger application. If not, I'd run the code as a windows scheduled job, cronjob, or a time triggered azure function. Something like that.