Depends on what layout you are using, but I'll assume you are using the default layout (BlueAndGreen).
- Open the clock cell
- In the Property Groups pane (left side), press the New button
- Give a name for the property group ("30s warning"?)
- In the Property Groups pane, the new property group (warning) should be selected
- In the Properties pane (right side), set the background color to your preferred color for 30 seconds left
- Click the Even Rounds tab
- Press the Delete Property Set button
- Click the Breaks tab
- Press the Delete Property Set button
- In the Property Groups pane, press the Conditions button; this will open the Edit Property Group Conditions dialog
- In the Stage pane, select Any Stage
- In the Conditions pane, for Seconds remaining, select "<=" (less than or equal to) and put 30 in the blank
- Press OK
- Press OK
Now, repeat those steps, replacing the name with a new name ("1m warning"?), and replacing the color with the color it should be at 1 minute, and replacing "30" with "60". You'll end up with two new property groups, "30s warning" and "1m warning". The 30s warning group should be listed above the 1m warning (if not, you can use the arrow keys to rearrange them). This is important, because the "conditions" will only match the "1m warning" group at 1 minute left, but the conditions will match both of them once the clock hits 30 seconds left. So, you want it to find the "30s warning" at that time and stop looking for a matching property group...
A lot of work, but that's the price of flexibility. But do it a few times and you'll get the hang of it.