There's a cell in this layout called "time of day". Edit that cell. The contents look like this:
<sp> <currentTime format="24-hour">
If you just remove the format part, you'll get a 12-hour clock:
<sp> <currentTime>
Because this layout makes extensive use of transparent backgrounds, it becomes a little difficult to deal with in the layout tab, as you can't read all of the cell names. To help, you can press the Preferences button on the Layout tab and then uncheck the box next to Stylize preview.
Sorry to jump in for you Stuart but I wanted to point at that last bit that I thought might be helpful.