Sonoff Dual control both channels with one rocker switch

Hi All!
First post. UK guy, and I hope this is on the correct forum.
I’m planning moving my multiple sonoffs to Home Assistant ESP Home, but have a wee question that I can’t find answer to in the meantime.

I want to run a fan and light, in 3 bathrooms, which are triggered from one external rocker switch. The idea being to set a timer on one channel, so that the fan only comes in between say 10 pm and 5am.

But I will be damned if I can find any info on setting the unit to work both channels with one external rocker switch.
Has anyone done it?