@Ted368 You should never decline an Inquiry. If it isn't a booking you want to pre-approve, just message the guest back within 24 hrs. No dates wil be blocked.
You only have to either accept or decline Trip Requests within 24 hrs, not Inquiries.
Or try to get the guest to withdraw the Request, so you won't have to decline.
And declining bookings simply because you are hoping to get another where the dates work better for you is not the way to run the business- if you decline a lot, Airbnb will suspend your listing.
You can create only certain check-in, check-out days and stay lengths using rule sets in "professional tools".