First of all, I'm not sure why you would want or need to pay for additional cleaning. The villas are like your own home, and come with all the cleaning tools and products necessary to do do any touch up from your kitchen duties and laundry duties etc.
Frankly, we prefer to not have housekeeping in at all. Trash and towel day they aren't in there very long, so that doesn't bother me, but I hate having to worry about if I'm out of the room when they come to clean.
If you are staying 7 nights, you will have trash and towel on the 4th day (counting check in as day one). If you are staying more than 7 nights, you will get a full cleaning on day 4 with a full change of bed linens and towels. If you stay 9 nights, you will have Trash and Towel on day 8.
In 14 years of membership, I've only requested an extra cleaning once, and that was when we had a change of guests mid-week.
I just like to be left alone so I can enjoy my vacation home without intruders. I don't change the beds more than once a week at home, so no need to change them more often than that on vacation. I also make my bed as soon as I get out of it at home, and I do the same on vacation. I hang my towel and use it for a couple of days, so that is covered too. The only thing I sometimes wish is that they would supply additional kitchen towels, as I seem to always get my kitchen towels dirty too quickly.
If you want to pay for additional cleaning, you can arrange that at the check in or call housekeeping from the room.