J. “Day” means a period of time from the hours of 0001 to 2400 based upon the local time of a pilot's domicile.

Many pairings are not paid correctly. Check your pairings and see if you have a 0000 show time on your first day. On a multi day pairing, Spirit owes you an additional 4.5 hours of pay. Even if they change your show time, they still owe you because that's the pairing you were awarded. If the company will not comply, you will need to grieve it.