@Eileen60 There is a lot of confusion about this topic, I'm afraid.
Airbnb requires that all initial messages, be they Inquiries or Reservation Requests, be answered within 24 hours as a matter of customer service and courtesy towards guests.
But, in terms of a host's response rate, how you respond is important.
For Inquiries, all you need to do is answer whatever question is being asked. Airbnb encourages hosts to send a Pre-Approval or a Special Offer, but these are optional. When a guest sends an Inquiry their payment method is unaffected. Guests can send as many Inquiries to hosts as they want, then sit back and see what kind of Special Offers or Pre-Approvals they get. Then they can choose to accept the one that appeals to them.
Reservation Requests, on the other hand, are totally different. Why? Because the guest is making a committment to book and Airbnb places an authorization hold on the guest's payment method pending the host's decision to Accept or Decline. If the host Declines, the authorization is withdrawn and in some cases it can take some dates for it to be released. If the host Accepts, the authorization turns into a charge immediately. Since authorization holds cannot be held indefinitely, Airbnb requires a 24 hour response from the host. Also, the guest is essentially locked in, and cannot look elsewhere, until the host who received the Reservation Request makes a decision. For a guest, having to wait 24 hours for an answer could seem like an eternity.
Where some confusion arises is when a guest uses a Reservation Request to ask questions when they should have used an Inquiry for that purpose. Sometimes host and guests are in different time zones which makes asking and answering questions to take too long. In this case, the host should politely ask the guest to retract their request and instead use the Contact Host link to continue the discussion which can go on for as long as needed. Or, the host can decline the reservation request with a nice note to the guest to use the Contact Host link.
It is very incombent on hosts to know the difference between an Inquiry and a Reservation Request and to never let a Reservation Request expire with out Accepting or Declining. When this happens, Airbnb blocks the dates requested which is not a good thing.
If you have more questions, let me know!