This varies from airline to airline. In Emirates, there's no charge for Hold My Fare as long as you pay for your flight within 72 hours. If you decide not to go ahead with your booking, a small fee will apply. If you’re booking through the United airlines, you can select the farelock option that lets you hold the same price and date of travel. Ryanair airlines allows you to reserve a flight for 24 hours only. While booking with Lufthansa, you can reserve the flight for upto 48 hours.