How do I check-in for Southwest 24 hours checking in for your Southwest flight 24 hours before departure is simple. Visit the Southwest Airlines website or app, enter your details, and select your seat. Check-in opens exactly 24 hours prior to departure, so set a reminder. Early check-in ensures you get your preferred seat and speeds up your airport experience. Don’t forget to print or download your boarding pass after checking in. Enjoy a hassle-free start to your journey with Southwest!