Hosts have 48 hours to formally accept or refuse a booking request. You will be notified by e-mail of the status of your request.
More than half of booking requests are accepted within one hour of being sent. The vast majority of guests respond within 12 hours.
If an host confirms your request, you can then go to your Yestudent account and pay for the booking (unless you've registered your credit card while making the request, in this case, you'll be charged for the first host who accepts you).
If a host refuses your request or if it expires (after 48 hours), you will have to make other booking requests.