Apply the Transform to the individual hour markers and not the the entire Canvas:
for (int i = 0; i <= 12; i++)
{
Ellipse teckaa = new Ellipse();
teckaa.Height = 30;
teckaa.Width = 30;
teckaa.Stroke = Brushes.Black;
teckaa.Fill = Brushes.Black;
canvas.Children.Add(teckaa);
Canvas.SetTop(teckaa, 25);
Canvas.SetLeft(teckaa, 215);
RotateTransform otoceni = new RotateTransform(i*30, 230, 230);
//canvas.RenderTransform = otoceni;
teckaa.RenderTransform = otoceni;
}
And see Petzold for a really cool all XAML clock.