Flying with United Airlines is an absolute breeze. United Airlines Check-in time for domestic flights opens up to 60 minutes prior to departure. International travellers are encouraged to arrive at least 90 minutes in advance of their flight, which ensures plenty of time to go through all the necessary procedures. Plus, if you're flying economy class and departing from the U.S., you can even access their online check-in system 24 hours before take off so you don't have to wait before boarding your flight! What's more: passengers are also given free access to several lounges, priority boarding and fantastic offers on seat upgrades - making air travel a whole lot easier and more enjoyable!