@Tan50
Since your advance notice is 3 days in advance your guest couldn't instant book 2 days in advance (even if you have instant book option) but he can send you an inquiry.
It is the same for all guests who don't meet your booking requirements for example travel with kids or pets and you have no-kids, no pets house rule etc...
If he sent you an INQUIRY and you don't want him to book then you can just answer in the text but if you want him to book then you should pre-approve him.
If he sent you a REQUEST then you have to accept or decline
Declining an INQUIRY has no consequences for you
Declining to many REQUESTS can have an impact on your search ranking, your acceptance rate and your instant-booking option which can be withdrawn