@Ory2I'm afraid its not possible! It is possible on other platforms you can put a nightly charge or weekly charge but not here.
I wish someone will post here and tell me I'm wrong.
I totally agree with you, I would like to put a WEEKLY charge for either changing the sheets or leaving an extra set of sheets on site. Laundering sheets is super, super expensive.
When people book over 1 week, you have to provide an extra laundry service, and you can't charge for it. On the contrary most people think they should be getting a discount for a long term booking!
At the same time my question is: why do you clean for them every day? Or is it just that you find longer stays make for more cleaning at the end (me too I find that).