Check in online is always better than waiting until the airport, as it is the quickest way to print your boarding pass and seal through the airport confidently. According to
Spirit airlines the best time to check in online is 24 hours before your flight and it ends 1 hour before departure. You can check in physically at Spirit Airlines' airport counter from 3 hours to 45 minutes prior to departure for domestic flights and from 3 hours to 60 minutes prior to departure for international flights.
