Checks in for your Southwest flight. Schedule this for a little bit before your 24-hour time and it will run until it succeeds, and get you an early boarding number and therefore a good seat.

southwest.sh

# POSTs your confirmation key, first name, and last name 
# to Southwest.com check-in endpoint over and over 
# until it doesn't see the 24-hour error.

# In testing I never got rate-limited or blocked
# but I didn't let it run for very long at a time
# so use at your own risk. :)

# Six-character SW confirmation token here
CONF=AB1234

ENDPOINT=http://www.southwest.com/flight/retrieveCheckinDoc.html

# Just in case they block more aggressively based on UA (I doubt it)
UA="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.62 Safari/537.36"

check_output() {
  while read stdin;
  do 
    match=$(echo $stdin | grep "more than 24 hours prior");
    if [[ $match != "" ]]; then
      echo "Failed to check-in for $2... trying again"
      run $@;
      return 0;
    fi
  done;
  echo "Successfully checked in on behalf of $2"
}

run() {
  curl --user-agent $UA --data "confirmationNumber=$1&firstName=$2&lastName=$3" $ENDPOINT | check_output $@;
}

run $CONF Artur Sapek