seems to work...

check_timestamp.rb

@@ -0,0 +1,20 @@
+class CheckTimestamp < Scout::Plugin
+  def build_report
+    begin
+      threshold = option(:threshold).to_f
+      path = option(:path)
+      timestamp = File.new(path).mtime
+      current_time = Time.now
+      difference = (current_time - timestamp) / 60
+      output = "Path: #{path}, Threshold: #{threshold}, Timestamp: #{timestamp}, Current Time: #{current_time}, Difference: #{difference}"
+      report(:output => output)
+      if difference > threshold
+        alert(:subject => "File #{path} was older than #{threshold} minutes", :body => output)
+      end
+      return difference
+    rescue Exception => e
+      error(:subject => 'Error running Check Timestamp plugin', :body => e)
+      return -1
+    end
+  end
+end

check_timestamp.yml

@@ -0,0 +1,9 @@
+options:
+  path:
+    name: path
+    notes: path to the file which will have its timestamp checked
+    default: /fully/qualified/path/to/your/file
+  threshold:
+    name: threshold
+    notes: threshold in minutes for the timestamp.  If the timestamp of the file is older than this threshold, an error will be returned.
+    default: 360