Spirit Airlines have enabled their passengers to check-in 48 hours prior to the original or current scheduled flight departure. Flyers of Spirit Airlines may simply select a seat, order the current dietary options available, as well as passengers, can take the advantage of the last-minute upgrade at check-in. Other than this, all the flyers still have to go through Spirit flight check-in at the airport, so that the airline chief can verify the travel documents and issue a boarding pass.

Know about: Spirit airlines check-in time

https://airlinespolicy.com/check-in-policy/spirit-airlines-check-in/