@Lorne-And-Marian0
Welcome to hosting!
You are doing a good thing to try to follow good hosting practices; and you are not the only one to be confused by the whole Response Time / Pre-Approve / Decline issue.
First things first:
Of all the options available to you, pressing the Decline button for everyone is probably the one option that would hurt your ranking the most... not to mention hurt your bookings also!
On to the details:
The conventional wisdom has been that for Inquiries (where the buttons say "Pre-Approve" and "Decline") you just have to send back a message to fulfill your obligation to respond. Experienced hosts replied via a message, and did not touch either the "Pre-Approve" or "Decline" button, and their Response Rate was always 100%. (This is my preferred course of action.)
Recently, the Airbnb help page about Inquiries was changed to say that a host had to press one of the buttons within 24 hours for it to count as a host response; a message was not supposed to be enough. However, subsequent testing by hosts demonstrated that the old method of just sending a message still worked. For some hosts, after sending a message they could even refresh the page and the countdown clock would be gone.
If you *do* have to push a button, don't just press the "Decline" button. Only press the "Decline" button if your really do not want the guest to stay with you. Otherwise, I just press the Pre-Approve button but send a discouraging message. An example: "Thank you for your inquiry! We do not offer any discounts; we feel our price as presented represents a great value." but send a Pre-Approval.
Don't worry too much though; pressing the "Decline" button for Inquiries is not a big deal.
However, pressing the "Decline" button for Booking Requests *is* a pretty big deal. But that is another topic for discussion.