Try an "If" action with a "Script" condition:
...where the result is 1 when the timer is running, 0 if not (because there will be 0 menu bar items with the description "Timer").
The AppleScript is:
tell application "System Events"
tell application process "Control Centre"
return count of (every menu bar item of menu bar 1 whose description is "Timer")
end tell
end tell
