Setting text property of a TextField

Ok, I'm kinda lost, I have a TextField and I want to set it's text property to a new text. But when I do it, the TextFild.text gets set, but is not beeing displayed.

the code so far

private var tf:TextField; 
public function setGame():void { 
     if (upcoming == true) {
          tf = new TextField();
          var tFormat:TextFormat = new TextFormat();
          var tFont:Font = new Dota2();
          tFormat.font = tFont.fontName;
          tFormat.size = 48;
          tFormat.color = 0x323232;
          tf.x = 230;
          tf.autoSize = TextFieldAutoSize.CENTER;
          tf.text = "Next Match In"; // thats beeing displayed
          tf.setTextFormat(tFormat);
          tf.embedFonts = true;
          addChild(tf);
     }
}
private function timerUp(e:Event):void {
     tf.text = "Next Match Is About To Start"; // text just disappears
     removeChild(clock); // this gets executed
}

Maybe I do something wrong with the order of the code or something.