I have found that a simple on/off switch for a fan with an overrun timer works just fine.The first of those ideas is more hassle, and requires more memory, than most people probably want!
Yes, you have to remember to turn it on when you go to have a shower, and off when you've finished, but it's not long before those actions become so automatic the you don't forget.
I have only one word to say to that.I would imagine that the on-delay is meant for 'nocturnal pees' (hence the usual fixed 2 min delay) and that they assume, rightly or wrongly, that generating smells(plus hand washing etc.) usually takes more than 2 minutes!
Asparagus.