MQTT - Auto Timer

I have a question regarding Shelly-1 and how to set the timer in MQTT, so that the relay goes OFF after TT seconds. I'm using NodeRed as my control environment.

I can get the relay to operate via http, using: http://IPaddress/relay/0/?turn=on&timer=2 , but alas not over MQTT.

So far I've tried using the following topic in the MQTT node: shellies/shelly1-my_mac/relay/0/timer with TT seconds in the payload but it has no effect.

Note that I can turn the relay ON and OFF via MQTT but I can't get the auto-off time to work,

I would appreciate any insight into how to make this work.

Seven of Ninbe - many thanks for your response.