If your performance collection level is set to "Transaction count and inline time" in your configuration, you will get additional information about the time spent inline in each rule. The following is an example from the Qwerty rules:
The time shown is always in ms (milliseconds) per transaction. If the time measured is less than 1 ms, 0 is shown.
Performance numbers below 10ms are shown in green, 10-50ms in yellow and more than 50 ms as red.