Let's not get into the technicalities of "Instant Book" and "Request to Book". They are mutually exclusive. Long story short: 

Instant Book boats don’t require approval from the owner before they can be confirmed. Client’s simply choose the date and time, as well as number of guests, and they are guaranteed to secure the boat once payment has been verified. 

Request to Book, however, will require owners to reply on the availability. This is usually completed within 24 hours. During this time, no payment will be deducted from your credit/debit card.