Knowing the correct timing for Spirit Airlines check-in is crucial to avoid unnecessary stress. Online check-in opens 24 hours before the scheduled flight, but it’s advisable to complete it as soon as possible to secure the best seats and avoid long airport lines. If you are checking in at the airport, aim to arrive at least 2 hours before domestic flights and 3 hours for international flights. Keep in mind that the earlier you check in, the less likely you are to encounter long queues at the Spirit Airlines check-in counter.
Source : https://www.flightaura.com/check-in-policy/spirit-airlines-flight-check-in-policy/