How to disable timeout in diagnostics aggregator?

edit

To cut down on CPU and message traffic, I modified the dignostics publishing in my system to only report ERROR messages, and not OK messages. However, now the diagnostics viewer is showing several topics as "stale", even though I've set timeout to -1 as mentioned in the docs.

My analyzers.yaml looks like:

pub_rate: 1.0
base_path: ''
analyzers:
  sensors:
    type: AnalyzerGroup
    path: Sensors
    analyzers:
      imu_calibration:
        type: GenericAnalyzer
        path: IMU Calibration
        timeout: -1
        contains:
        -   imu_calib

and the diagnostics viewer is showing an item called "Sensors->IMU Calibration = STALE". Why is this?