is timer thread-safe?

[the one]

Let's say we have 3 timers started by 'SetTimer' on a single window. So we have 3 different static TIMERPROC function.

i.e.

CMyWindow::OnInitialUpdate()
{
...
SetTimer( 1200, 500, (TIMERPROC)Function1 );
SetTimer( 1300, 500, (TIMERPROC)Function2 );
SetTimer( 1400, 500, (TIMERPROC)Function3 );
...
}

//static
UINT CMyWindow::Function1( ... )
{
...
}

and others...

Is there a possibilty of calling any two of Function1, Function2 and Function3 at the same time? Are they processed by a single thread or by three different threads?