For those who did Visual Basic 6, you must be familiar with using timer control in your application. Just drag and drop the Timer from the Toolbox:

Then start writing code, just set the Interval of the timer in design time or run time.
For this example, the timer is set during run time:

Private Sub Form_Load()
    Timer0.Interval= 3000
    Timer0.Enabled=True
End Sub

Public Sub Timer0_Timer()
    Beep
End Sub

And you will get this Form1 application running: (It is best if set Timer control to Visible=False)

But how about using timer in other programming language? For example, in native Windows, C++ code can directly access the Win32 API to set and kill timer with callback.

Below are some example code taken from: https://learn.microsoft.com/en-us/windows/win32/winmsg/using-timers

Creating a Timer:

// Set two timers.

SetTimer(hwnd,             // handle to main window
   IDT_TIMER1,            // timer identifier
   10000,                 // 10-second interval
   (TIMERPROC) NULL);     // no timer callback

SetTimer(hwnd,             // handle to main window
   IDT_TIMER2,            // timer identifier
   300000,                // five-minute interval
   (TIMERPROC) NULL);     // no timer callback

The callback to the GUI window is through WM_TIMER message in the window procedure.
(We have to familiar ourselves with window class, window procedure, message loop, message queue while working with GUI window in Windows)

case WM_TIMER:

   switch (wParam)
   {
       case IDT_TIMER1:
           // process the 10-second timer

            return 0;

       case IDT_TIMER2:
           // process the five-minute timer

           return 0;
   }

Or if initializing the timer with callback to your own TimerProc procedure, the parameters to pass are a little different:

// Set the timer.

SetTimer(hwnd,                // handle to main window
   IDT_TIMER3,               // timer identifier
   5000,                     // 5-second interval
   (TIMERPROC) MyTimerProc); // timer callback

Destroying a Timer

// Destroy the timers.

KillTimer(hwnd, IDT_TIMER1);
KillTimer(hwnd, IDT_TIMER2);
KillTimer(hwnd, IDT_TIMER3);

This is the screenshot of the GUI window with timer I created in FASM:

(It will beep every 3 seconds, but I am not posting the code on here anyway)

WM_TIMER is a low-priority message among window messages like WM_PAINT.
Make sure messages like WM_PAINT does not block the message queue, or else WM_TIMER message cannot be read.

Do you have other example of programming language to share, as to how to use timer in your software project?