How to set up fan timer mode with Blue Fan Switch?

Today I got several Blue Fan Switches which I’d like to use as a bathroom fan timer with Home Assistant and zigbee2mqtt and thought I’d have to do this with complicated automations, but in the settings for the switch I see Fan Timer mode which sounds like just what I am looking for, but I’m not sure how to set that up. The switch should control simple on/off with no speed control.

For temporary setup purposes I have the switch in a tabletop box with line, neutral, and ground hooked up but no load for now. I did change some settings in the zigbee2mqtt exposes screen before I found the Fan Timer mode so I’m not sure if I did anything incompatible with that mode, if needed I can factory reset.

Looking at the parameters article I set mode high, single pole, led color when on/off to green, single tap new behavior, fan control mode to disabled, exhaust fan output mode, fanTimerMode enabled. But I’m not sure how the fan timer mode is meant to be used, if on the switch I press the top of the toggle it lights up all green (as configured) and if I press down the lights go off, and pressing the scene button seems to do nothing.

I was expecting to press something and have the LED bar graph start with 1 LED lit, then another one if I press again, then have it slowly go down as the timer decrements.

Are there details (or a video) explaining exactly how to set up and use fan timer mode?

There are two parameters that you can use to implement a timer on the switch. They are mutually exclusive, so use one or the other.

Parameter 12 - Auto-Off Tmer

This is the basic timer. Set the value to the number of seconds you want the fan to remain on.

Parameter 121 - Fan Timer Display

If you enable this one, multi-taps of the switch will turn on a timer for specific periods. Also, the LEDs will blink as a countdown timer.

See the parameter page for detals for each: