Hi @Savion0, I am not sure if there is a policy on this, although I think I read somewhere on the forums that Airbnb recommends you do a clean/linen change after a week. I don't know if that is actually true as I couldn't find any info on it when I searched the help section.
I think what services you provide in terms of linens, towels, laundry and cleaning are up to you, but it would be a good idea to make these clear from the start. A good place to do this is in your house rules. Make sure you message guests before booking to double check that they have read the full listing and house rules and agree to them. I see you are using Instant Book, in which case, the guests still have to agree to the rules in theory, but it's better to message them after booking to make sure.
This is what I do. If I have guests staying two weeks or more, I tell them I will clean their room half way through and offer them clean linen and towels if they want them. This also gives me a chance to check up on things and make sure the room is okay (I don't go in without permission if I can help it, because I want to respect their privacy). I once had guests stay at my old apartment for a month, and as I wasn't living there, I couldn't do this, so just told them to use the laundrette which was on site. However, I regret this because they never washed the linen or towels, which were brand new, and I had to throw them away as it was impossible to get them clean after that!
That's just me though. If you can't/don't want to do this, fine, but going forward, put in your house rules that you don't provide any laundry services and that long-term guests are responsible for washing the towels and bedlinen. You could include that you provide a card for the local laundrette, if this is something you plan to do regularly. If you want, you could also add that you can do laundry for an extra charge.
Whatever you decide to do, put it in your house rules, make sure they have read and agreed to them before they come and maybe run through the important ones again when they arrive. A lot of hosts leave a print out of the rules for the guests as well.
Hope that helps!