netatmo co peak reading time frame

I’ve recently installed a Netatmo CO sensor. It appears to be working fine, but I’ve spotted it has a peak level (8ppm). It has been in this for a few days, I’m curious on the time frame of this. Is the peak level stored by the device and sent to HomeKit or is this a peak level stored by HomeKit, either way I’d like to know when it should reset. Thanks.