Not sure if you are aware of how SW boards. There are three lines....A, B, and C. In each group there are about 50 or so slots..perhaps more, I just forget the actual number. When you check in at the 24 hr window, you will get a boarding pass slot for each member of your group. Then, at the gate, you will be called, by letter grouping, to take your place in the corresponding slot. There are poles setup with numbers on them, within each letter group...1-5, 6-10, 11-15- 16-20 and so on. When you get to the end of that letter grouping and all are boarded, they call the next letter grouping up.
Those with any medical issues board first, before anyone else. Also, unattended minors flying. Then, those who have paid the refundable fares (business select) board. They are given the A1-15 slots. Then, everyone else is boarded. Those flying with kids under the age of 4 are allowed to board inbetween the A and B groups..if they didn't get an A slot.
So....with that in mind. SW now has Early Bird Checkin. You can pay an addlt $10 pp, per flight. This will allow SW to check you in at the 36 hr window vs the 24 hr window you normally use. You don't need to do anything...SW does it for you. You are checked in according to when you bought EBCI. Those who booked it 5 months before their flight will get a lower slot than those who booked EBCI 2 months prior. There is no way to tell exactly how low a slot you will get though. But, you will get a slot before those who are booking at the 24 hr window. Are you assured of an A slot? No, but you will most likely get one.