@Sarah977.. I raised exaclty this question in the german CC .. because I also thought that the wording is not that clear. I got the answer from our admin that both options are opt-in options and you won't have to opt in in one or the other either. If you don't opt in in the 24 hour cleaning protocol your calendar would not be blocked for 72 hours. Both options are facultative to give the guests some 'peace in mind'. Further I got the info that both protocols are not available for shared places.
https://community.withairbnb.com/t5/Gastgeber-unter-sich/Neues-cleaning-protocol-ab-Mai/td-p/1287258
Also in the english CC I read from one whose husaband or father or something is an attorney and he also admit that the wording is tricky but both are optional opt-ins ... I guess the wording is tricky that the guests feel more safe...
Despite the ranking .. yeah .. that could be .. but at the end of the day, airbnb is only interested in selling .. so, if your property is for interest for many people, the cleaning protocol would be less important .. jm2c.
@Alexandra199... it seems that with 3 days we are on a quite safe side for most sufaces. We also have to distinguish between studies which found 'the virus' after some days .. this does not peremptory mean that the virus is still infectious as the genome lasts longer than the surrounding envelope .. but without envelope the genome is not harmful. But yeah, probably a small risk lasts longer than 3 days. Anyway .. you could not disinfect everything, best is to regard an accomodation the first three days as public space .. means, don't touch your face with unwashed hands.