In most cases you find out straight away, but not every booking works that way. The majority of rates coming through a hotel API are instant confirmation, which means the supplier holds live availability and sends back a confirmation reference within seconds of the payment going through. Your portal shows the booking as confirmed, the voucher becomes available, and your customer can be told the room is secured.
Some rates are what suppliers call on request. With these, the booking is passed to the hotel for acceptance rather than confirmed automatically, and your portal will show it as pending or awaiting confirmation until the hotel replies. This is more common with small independent properties, certain directly contracted rates, and larger room blocks. How long the hotel takes to answer is entirely up to the supplier and the property, so that is not something we can promise on their behalf. Whether on request inventory appears in your results at all depends on which suppliers you are connected to.
The practical advice is to treat a pending booking as not yet secured. Avoid issuing the voucher, taking the booking as final, or letting your customer buy a non refundable flight around it until the status changes to confirmed. If the hotel declines, the portal will mark the booking as rejected, and how the money is handled then depends on your payment setup and the supplier's own rules.
When you are setting up, ask us to show you how confirmed and pending bookings are labelled in your search results and booking list, so your staff can tell the difference at a glance.