This will be changed to allow you to push the Countdown button, and then it will tell you why the countdown can't start, to make it less confusing...
One way to add a custom message (there are several), is to create a new Cell, place your text in the cell, and put the cell on the screen where you want it displayed.
Easiest thing to do is copy an existing cell that has similar properties, so you don't have to change much. As an example, right-click on an existing cell next to which you'd like to place your new cell, and select Insert cell (above/below/before/after) ... /. In the "Copy" section, select the Tournament Info cell, give the new cell a name, and press the Copy Cell button. Double-click on the new cell and change the text (HTML) of it to your message. Make sure to do this (change the text) on each of the Property Set tabs (Odd Rounds, Even Rounds, Breaks).
If your message changes each tournament, you could insert one of the rules tokens instead, so that you could just change your message on the Rules tab each tournament instead of actually modifying the layout. For example, put the text "<announcements>" in the HTML of the cell instead of your message. Then on the Rules tab, change the text for the announcement rules token.