@Mary1746 Your dates will only be blocked by Airbnb for other bookings if you cancel a reservation, not if you just decline a Booking Request or are able to get the guest to withdraw the request. And they don't get blocked at all for Inquiries- on an Inquiry don't ever decline- just message the guest back within 24 hours, that's all that's necessary.
So if you use Instant Book and have to cancel a reservation, then the dates will be blocked, as I don't think Airbnb will consider your reason for cancelling to be a valid one.
I'm not sure I understand your question completely, though. Why would you have dates available on your calendar if you can't accomodate guests on those dates?