I agree with Dede. Just two nights ago, I received a Booking Request from a Guest who wanted to bring a dog. (We're not dog friendly.) I immediately wrote back and asked a couple questions about the dog, etc., and then wrote again about 10 minutes later. 14 hours later, they wrote and said that they couldn't stay and I asked them to withdraw their Request. I didn't know that they didn't withdraw (or maybe you can't withdraw a Booking Request???), and EVEN THOUGH I HAD REPLIED QUICKLY, the Booking Request expired and I had not Accepted or Declined. I immediately received an Airbnb email saying that because I had not responded (and I had) that those dates were now blocked on my calendar, and that the position of my listing might be affected. So, yes, you do need to Accept or Decline within 24 hours or have those dates blocked on your calendar, at the least. Good Luck.