A "Request To Book" campground allows the campground up to 24 hours to accept or decline your reservation request. Upon submitting a "request to book", you will receive an email about the "request" with the note about allowing 24 hours for a response. Once a booking has been accepted, declined or even if it has "expired", you will receive another email about the status of that request.
Depending on your email provider, this can end up in spam. Please check your spam folder if you don't see it.