In-Line extract fan humidity sensor

[Robbox]

We have an inline fan to extract the bathroom, it has a timer fitted and runs when the lights go on.
I'd much prefer to operate the fan independently of the light switch, either by a PIR or humidity sensor. Done some research and it seems there are very few switches of this type available and they all have a timer as well.
From what I understand, the switch timer will interfere with the fan timer.
Are there any other solutions? Can the fan timer be bypassed?

 

[Taylortwocities]

Fan timers can be bypassed. It does depend on the fan, and how handy you are with a soldering iron.

 

[AndyPRK]

or just turn the time down to 20 seconds or so, and you won't notice the difference!

 

[winston1]

From what I've heard humidity sensors are a bit hit and miss.

 

[AndyPRK]

my manrose one needed a lot of adjustment, but I like the benefit