Hi @Jadelyn1
Just as an example, I have Instant Book turned on and I take bookings by setting the calendar to "At least 1 day". So if a guest books more than 24 hours before my check-in time, the booking goes through instantly. However, I also have that slider button on that shows in the screenshot "allow requests with shorter notice". So when guests want to book less than 24 hours before my check-in time, it comes through in the form of an enquiry (instead of an instant booking), which I can then approve. This gives me a few moments to think whether the place will be ready on time, or to ask them what time they plan to arrive.
Hope it helps to clarify how it works at a practical level.